Reply
 
Thread Tools Display Modes
  #1   Report Post  
John L Stewart John L Stewart is offline
Senior Member
 
Location: Toronto
Posts: 301
Smile Sequel to Low Cost SET Amp for Newbies

At 130 views & counting it seems like we need a follow on. So here it is with more power. This was originally published in the Glass Audio Projects Book, April 2002, along with 16 other vacuum tube designs. The space on AudioBanter is tight, so some of the information will appear in a following post.

MORE POWER FOR THE AFFORDABLE SE AMPLIFIER

While working on the earlier Affordable SE Amp (GA 4/00) it occurred to me there might be an easy way to get even more power with only a slight increase in cost.

All single ended amplifiers need to run in Class A mode if they are to deliver good quality sound. In order to do that they need to be capable of dissipating considerable heat. Tubes in the list for the original low cost SE Amp barely fit that requirement. However, several compactrons with a beam tetrode & high mu triode in a single envelope are available on the NOS market at reasonable cost. See Table One. They have power handling ability at about 50% better than those on the previous list. To further this project, I selected the 6LU8.

CIRCUIT FEATURES

1) Operation in Triode or Ultralinear mode.
2) Operation with or without feedback.
3) Power frequency hum cancellation.
4) Start/Standby & Run Modes.
5) Excellent performance.
6) Low cost has been maintained.

TRIODE OR ULTRALINEAR?

The original amplifier used a low cost Hammond 125E for it’s output transformer. That transformer has a center tap which could be connected to the screen of the beam tetrode, thus providing a degree of ultralinear operation. I arranged layout of the various parts so that a comparison of performance could be made between triode & ultralinear topologies. Referring to Figure one see that the screen grid of the beam tetrode is shown unhooked. You can make a connection either direct to the plate (triode operation) or to the 125E center tap (ultralinear).

CAUTION- Don’t use a switch to make the circuit change. Energy stored in the magnetic field of the 125E tries to keep current flowing. You could cause a failure of the insulation in the transformer because of the large induced voltage caused by switching. When you make the change your amplifier should be completely disconnected from the power source.

At midband the resulting amplifier delivered 5 watts in triode mode & 6 watts when connected for ultralinear operation. Refer to Table Two for a summary of performance of the various configurations.

THE MODIFIED AMPLIFIER

As shown in the schematic the amplifier is connected so that all of the gain is used by feedback. If you would like to run without feedback then unhook R4 from terminal one of the 125E & connect to COMMON. You will also need to remove C3 & R5 from the circuit & connect C2 to the junction of R6 & R7.

The coupling cap between the voltage amp & the power amp becomes more critical as more feedback is used. You are normally told to use as large a coupling cap as practical at this position. However as feedback is increased
a hump will appear in the low frequency response. I measured up to 4 db rise at 30 to 40 Hz. C3 & R5 provide a step in the low frequency response. This allows more feedback to be used without instability.

An important addition to this amp are three grid stopper resistors. This tube has very high transconductance & will likely oscillate on it’s own if given a chance. I knew I had problems when my FM receiver was interfered with
while the amplifier was running. I observed spectrum up to 150 Mhz. Grid stopper resistors lower the Q (Quality Factor) of the circuit according to the formula

Q = (1/R)  SQR ( L/C )

As little as 100 ohms in a conductor interferes with the RF to the extent that it is eliminated. The audio is left intact.

The remaining LF time constant in this amplifier is the filter section of the power supply. Many experimenters either ignore this one or simply follow the lead of others. However, it is in the audio path & does have considerable effect on the final result.

For triode operation connect an 8 ohm loudspeaker to terminals 2 & 6 of the 125E. If you would like to use the ultralinear mode, then you can connect an 8 ohm loudspeaker to terminals 3& 6.

THE POWER SUPPLY

You will need more power for this version of the SE Amp. Here it is supplied by a Hammond 271X transformer. Filtering is provided by a PI section consisting of a Hammond 156L, 5 Henry choke & a pair of 100 microF caps.
This time the caps are rated at 450 volts working. Refer to Figure 2.

The filter section is resonant at 10Hz. That has an effect on the low frequency performance of the amp. A simple regulated power supply would eliminate this problem. Perhaps next time.

A current sampling resistor of 10 ohms is in the center tap lead of the HV winding. Using a X10 probe I measured peak current of 250 mA on the scope. Average current was 70 mA.

The pilot light has been moved to the 5 volt winding to somewhat relieve load on the 6.3 volt winding. However, total load is well within the capabilities of the 271X. I measured input to the power transformer to be
46 VA* in the run mode. In standby it was 20 VA. The 271X is rated for 63 VA input.

A Start/Standby mode is provided by the 3PDT, center off switch S1 sections A, B & C. Diode ring D3 thru D6 sets the heaters to about 4.9 volts when S1C is open. C105 & C106 are Mallory part number UN103M. These caps are Underwriters Laboratory approved for across the line applications.

POWER FREQUENCY RIPPLE CANCELING

In a previous article (GA 3/98) I had described a simple addition to the power supply circuit which would almost eliminate the power frequency hum component. That would be 60 Hz in North America & 50 Hz in Europe & elsewhere. This component of hum results often when a centertapped transformer is used in the power supply.

Two halves of the HV winding may not be balanced for resistance. For example, in the Hammond 271X the two sides of the HV winding measured 167 & 142 ohms. The power frequency ripple happens to be in the same range as the resonance(s) of most loudspeaker systems. This sometimes causes problems in systems using SE triode amps. Here is a practical application of that circuit.

You will find the fix in this amplifier easy to make. The 5 volt winding is connected in series with the center tap of the HV winding. The extra 5 volts will be series aiding for one side of the HV winding & series opposing for the other side. There are no polarity markings on most power transformer leads. On the first try there is an even chance the hum will get worse.

Your best check for the proper connection is by using an oscilloscope. Connect the scope probe to the ungrounded end of the 10 ohm resistor (TP A) in the center tap return lead. Proper connection of the 5 volt winding results in the current pulses all having about equal amplitude. If you have connected the 5 volt leads the wrong way, alternate current pulses will have somewhat different heights. Refer to Figure 4.

When connected properly I measured a 12 dB reduction of the power frequency ripple as compared to the normal hookup. It cost us nothing.

If you don’t have an oscilloscope to make this adjustment, two other kinds of measurement are possible. A peak responding AC voltmeter such as the HP 410A, 410B or 410C could be used to measure the voltage peaks produced across the current sampling resistor. Correct connection of the 5 volt winding leads is that which produces the smallest voltage. This will vary depending on your circuit but will be in the range of 2.5 volts.

Finally, you can build your own simple peak responding voltmeter. See Figure 4. Most any signal or power diode will work. From my junk box I tried a 1N4007 as well as a very old 1N56A. The 1N56A is a Germanium device so has a smaller forward drop. It worked best. The external VOM of 20000 ohms per volt was set to the 3 volt range. Connect the 5 volt winding leads to give the lowest reading when connected to the test point on the 10 ohm sampling resistor. Indication will be about 2.5 volts.

LINE STAGE

When you use the feedback version of the amplifier you will find the gain to be somewhat low. In order to get enough gain most experimenters will try three stages of gain. Instability often results when feedback is connected. Even the famous Williamson amplifier exhibits some low frequency problems since there is too much gain & phase shift inside the feedback circuit.

A simple line stage can easily fix this problem. Refer to Figure 3. This is an application were a pair of feedback amps are connected to provide enough gain without instability. As shown the line stage has a gain of 8.

CONCLUSION

Was the project worth the time & effort required? I would say yes. For a very reasonable cost the amateur can get some experience of what vacuum tube audio is really about.

In my various designs I try for synergy. That is to say the various parts should somehow compliment each other so that the final result will easy to implement, safe & reasonable cost. All designs will have some tradeoff’s.
The designers job is to separate those which are important from the rest.

The primary objective I had in mind with the Affordable SE Amp was to illustrate what is possible on a tight budget. I wanted to avoid exotic & otherwise expensive components which seem to be running rampant in the present vacuum tube audio revival.

For those who would care to spend a little more money the most effective improvement they can make to this design is a better output transformer. The Hammond 125E was not designed with high fidelity in mind. I would recommend the Hammond 1628SE. You will get a large improvement in the low frequency response. Distortion at all levels would be reduced since the 1628SE is specially designed for single ended applications. Refer to Table 3 for some comparative distortion measurements made at 100 Hz.

*VA- Volt-Amperes
Attached Images
  
Attached Files
File Type: doc Table One Summary of Power Tetrodes.doc (19.5 KB, 336 views)
  #2   Report Post  
Posted to rec.audio.tubes
Stephie Bench Stephie Bench is offline
external usenet poster
 
Posts: 10
Default Sequel to Low Cost SET Amp for Newbies

Hi John,

Very nice. A couple of comments. On the screen stopper, sometimes you can get a "free" improvement in performance by tailoring the value of the stopper resistor. I think, but I am not familiar with that tube, that a slightly larger resistor may improve the distortion, particularly at moderate power levels. The second comment is the cathode bypass cap. Depending on its overall quality, bypasing that cap with another non electrolytic, say 1 or 10uF polyprop will both improve HF performance, and often lower distortion, since it removes the nonlinear effects of the cap.

Thanks for publishing those.

One further note in general note on low cost SE amps. By using a tetrode or pentode connected in triode (or UL) mode, you often get the benefit of a subtly better (more precisely, lower order) plate resistance linearity. This often doesn't particularly show up in static distortion measurements, but under the condition of a reactive load, it produces lower distortion. Nice benefit from using a "cheap" tube. You can ve4ify this by making your static load reactive somewhat, and measuring the distortion in that condition.

Stephie
  #3   Report Post  
John L Stewart John L Stewart is offline
Senior Member
 
Location: Toronto
Posts: 301
Default

More information here on the SET Sequel-

Equipment used in the development of this amplifier-
HP 200CD Oscillator
HP 302A Wave Analyzer
GW GAG-810 Oscillator
Rohde & Schwarz BOL 4 Trace 100 MHz Scope
RS 22-168A DMM
Sanwa AX 303-TR Analogue Multimeter
PicoScope ADC-100 Virtual Instrument
Electronic Workbench Software

For a schematic of the simple line stage used refer to my post of Jan 8th

Cheers to all, John L Stewart
Attached Files
File Type: doc Table 2 Summary of Performance at One KHz.doc (19.5 KB, 224 views)
File Type: doc Table 3 Comparison 125E vs 1628SE.doc (19.0 KB, 210 views)
  #4   Report Post  
John L Stewart John L Stewart is offline
Senior Member
 
Location: Toronto
Posts: 301
Default

And still more.

Cheers to all, John L Stewart
Attached Images
 
Attached Files
File Type: txt GA28PARTS Z.txt (903 Bytes, 247 views)
  #5   Report Post  
John L Stewart John L Stewart is offline
Senior Member
 
Location: Toronto
Posts: 301
Smile

Quote:
Originally Posted by Stephie Bench View Post
Hi John,

Very nice. A couple of comments. On the screen stopper, sometimes you can get a "free" improvement in performance by tailoring the value of the stopper resistor. I think, but I am not familiar with that tube, that a slightly larger resistor may improve the distortion, particularly at moderate power levels. The second comment is the cathode bypass cap. Depending on its overall quality, bypasing that cap with another non electrolytic, say 1 or 10uF polyprop will both improve HF performance, and often lower distortion, since it removes the nonlinear effects of the cap.

Thanks for publishing those.

One further note in general note on low cost SE amps. By using a tetrode or pentode connected in triode (or UL) mode, you often get the benefit of a subtly better (more precisely, lower order) plate resistance linearity. This often doesn't particularly show up in static distortion measurements, but under the condition of a reactive load, it produces lower distortion. Nice benefit from using a "cheap" tube. You can ve4ify this by making your static load reactive somewhat, and measuring the distortion in that condition.

Stephie
Thanx for your comments Stephie. I’ve never tried adjusting the G2 resistor on the OP section. I simply used something less than one K in order that G2 can get what it needs while the plate is heavily conducting. I’ve been primarily interested in avoiding parasitics. G2 needs a lot of current when the plate load line goes up into the knee of its conduction.

But in real life the loadline is for the most part elliptical. And it can & does regularly pass thru a –ve rp region in the lower LH corner of the plate family. So that adjusting the G2 resistor for optimum would be worthwhile. Something to try!

During this project I tried the 6LU8 in straight pentode operation. It was somewhat less than ideal. Not recommended at all. But it was designed as a sweep tube, audio not in mind at all.

On the more recent projects I’ve included in parallel with the PS electrolytics better quality caps of say 0.1 to one microF for the reasons you’ve noted. But I’ve done no serious SE projects since these two.

For the Twin Coupled Amp (ie Norman Crowhurst) projects I put together a simple speaker simulator for stability, THD & IMD tests. I found that to be very useful. Keeps things quiet as well. Attached here.

Not much going on with toobz these daze. It is snowing again here out in the woods NW of Toronto. We had a huge ice storm just before Xmas so lots of trees down. The power was off for three full days. Later today I gotta get on the tractor again. And if Spring ever gets here the chain saw will be very busy!

Cheers, John
Attached Images
  


  #6   Report Post  
Posted to rec.audio.tubes
Patrick Turner Patrick Turner is offline
external usenet poster
 
Posts: 3,964
Default Sequel to Low Cost SET Amp for Newbies

John Stewart proposes a low cost SE amp using 6LU8.
http://www.audiobanter.com/attachmen...tachmentid=379

It is many years since that tube has been made. Maybe not everyone could obtain one. Pentode Pda rating = 14Watts, so say 12W max in practice for SE class A1. This means max Po = 5 Watts with low OPT losses, at 42% anode efficiency.

I suggest it would be easier to use say 6BQ5 driven by 12AX7 with its 2 triodes in parallel. Both are made now, and old stock is available.
The above schematic has the V1 triode cathode with 1k8 connected to whole OPT sec winding and for GNFB network. I humbly suggest there's a resistor missing between cathode and 0V; the whole GNFB network needs to be changed.
Of course if one does want a nice cheap 5 Watts, it is even better to use a single EL34 in triode, idling with Pda = 16W, and same paralleled 12AX7 as input / driver, and with say 12dB GFB. Then Ea might be higher, and RLa higher, but then any cheap amp with low Po should be extremely well thought about to compensate for its basic shortcomings of having not much Po. UL with EL34 is good - and for reasons Stephie mentioned; although they'd go right over most ppl's heads. UL Po could be 7Watts with Pda at same 16W at idle, same Ea and Ia. But RLa changes, so thought must be used if any benefit is to be heard.
If EL34 is considered, then minor bias change will allow 6L6GC, and the world is full of 6L6, EL34, 12AX7. I'm not sure how much goodness resides in the probably small cheap Hammond OPT.
Patrick Turner.



  #7   Report Post  
John L Stewart John L Stewart is offline
Senior Member
 
Location: Toronto
Posts: 301
Smile

[quote=Patrick Turner;976270]John Stewart proposes a low cost SE amp using 6LU8.
http://www.audiobanter.com/attachmen...tachmentid=379

It is many years since that tube has been made. Maybe not everyone could obtain one. Pentode Pda rating = 14Watts, so say 12W max in practice for SE class A1. This means max Po = 5 Watts with low OPT losses, at 42% anode efficiency.

------------------------------------------------------------------------------------

I had a quick look the other day. The 6LU8 is available for 6.70 USD while the 6EM7 used in the original project at 8.90 USD. And the 6BQ7 at a princely 1.70 USD, all at www.tubesandmore.com. So it looks like there is no availability problem at all.

------------------------------------------------------------------------------------

I suggest it would be easier to use say 6BQ5 driven by 12AX7 with its 2 triodes in parallel. Both are made now, and old stock is available.
The above schematic has the V1 triode cathode with 1k8 connected to whole OPT sec winding and for GNFB network. I humbly suggest there's a resistor missing between cathode and 0V; the whole GNFB network needs to be changed.

-------------------------------------------------------------

All well & good. If one looks at what is out there the number of permutations & combinations should work out to be about the third root of infinity! As I had commented in the original article, the objective was to simply illustrate a starting point a newbie could try for the SET type amp. At a reasonable cost.

---------------------------------------------------------------------------------------
Of course if one does want a nice cheap 5 Watts, it is even better to use a single EL34 in triode, idling with Pda = 16W, and same paralleled 12AX7 as input / driver, and with say 12dB GFB. Then Ea might be higher, and RLa higher, but then any cheap amp with low Po should be extremely well thought about to compensate for its basic shortcomings of having not much Po. UL with EL34 is good - and for reasons Stephie mentioned; although they'd go right over most ppl's heads. UL Po could be 7Watts with Pda at same 16W at idle, same Ea and Ia. But RLa changes, so thought must be used if any benefit is to be heard.
If EL34 is considered, then minor bias change will allow 6L6GC, and the world is full of 6L6, EL34, 12AX7. I'm not sure how much goodness resides in the probably small cheap Hammond OPT.

[quote]

----------------------------------------------------------------------------

For the cost it ain't bad. But as always, one can throw as much money at a project as they wish. I did suggest an improvement to a more costly Hammond. Since the original article was published Hammond have introduced an improved 125SE Series that would help. But it don't have a UL tap. So SEUL not possible with that one.

Cheers to all, John L Stewart
Attached Images
 
  #8   Report Post  
Posted to rec.audio.tubes
maxhifi maxhifi is offline
external usenet poster
 
Posts: 164
Default Sequel to Low Cost SET Amp for Newbies



Patrick Turner wrote:

John Stewart proposes a low cost SE amp using 6LU8.
http://www.audiobanter.com/attachmen...tachmentid=379

It is many years since that tube has been made. Maybe not everyone could obtain one. Pentode Pda rating = 14Watts, so say 12W max in practice for SE class A1. This means max Po = 5 Watts with low OPT losses, at 42% anode efficiency.

I suggest it would be easier to use say 6BQ5 driven by 12AX7 with its 2 triodes in parallel. Both are made now, and old stock is available.
The above schematic has the V1 triode cathode with 1k8 connected to whole OPT sec winding and for GNFB network. I humbly suggest there's a resistor missing between cathode and 0V; the whole GNFB network needs to be changed.
Of course if one does want a nice cheap 5 Watts, it is even better to use a single EL34 in triode, idling with Pda = 16W, and same paralleled 12AX7 as input / driver, and with say 12dB GFB. Then Ea might be higher, and RLa higher, but then any cheap amp with low Po should be extremely well thought about to compensate for its basic shortcomings of having not much Po. UL with EL34 is good - and for reasons Stephie mentioned; although they'd go right over most ppl's heads. UL Po could be 7Watts with Pda at same 16W at idle, same Ea and Ia. But RLa changes, so thought must be used if any benefit is to be heard.
If EL34 is considered, then minor bias change will allow 6L6GC, and the world is full of 6L6, EL34, 12AX7. I'm not sure how much goodness resides in the probably small cheap Hammond OPT.
Patrick Turner.


Decided to check out RAT after years absence.. not much left, but at least the arguments appear to be gone. I'll add my two cents to this topic, since it looks interesting (and maybe to enjoy contributing to usenet while it still exists!).

I think the amplifier looks like a great idea for a project... Sure someone may have a little trouble getting the 6LU8, but on the other hand old TV tubes are a great way to get NOS tubes on the super cheap. Supply is fairly minimal, but demand is even smaller still, so unless it becomes a national pastime to assemble cheap as dirt tube amplifiers, someone will be able to secure a pair of RCA or GE or Sylvania 6LU8 for well under the cost of a single quality 12AX7 (Perhaps living in North America is an advantage here). eBay is flooded with the 6LU8, and other similar tubes, and it avoids being forced to go
with either inferior modern production tubes, or high dollar desirable types of NOS which have likely been picked over. I understand it may be somewhat controversial to call modern tubes inferior to NOS, but a quality NOS tube is quite a safe bet from a reliability standpoint, considering they were made in the days tube tech was to be relied upon for communications between humans, rather than a pastime enjoyed mainly by eccentrics, people overcome by nostalgia, "connoisseurs" and obsessive musicians.

Also, it's kind of elegant to have a two tube stereo amp.

A salvaged output transformer from an old TV chassis would make this even cheaper, and it would be possible to figure out how much NFB it can take before instability sets in. Those Hammonds are the right ticket for this sort of cheap and cheerful effort, but I think they're priced about double what their real value is.

This amplifier would be right at home driving a paper cone speaker, for example, as a small scale computer hi-fi setup. Naturally the limited power output and small output transformer core would severely limit applications in a serious hi-fi context, but nobody would expect a $100 amplifier built of junk-bin parts to perform in the league of serious dollar equipment.

I would submit that the problem with a low cost SE 6L6 or EL34 amplifier, is to do it properly you would exceed the cost of a push-pull amplifier and at the same time suffer worse performance. I don't really see any value in it. A push pull transformer won't be gapped, so you avoid this cost plus get free cancellation of second harmonic distortion, and increased hum rejection all in one stroke by moving to push-pull. The special single ended sound (if it indeed exists) that some people rave about won't be captured at this price either, so all you really end up with, when you make a cheap SE 6L6 amplifier is an
amplifier that costs more than a push pull amp and performs worse.




  #9   Report Post  
Posted to rec.audio.tubes
mick mick is offline
external usenet poster
 
Posts: 10
Default Sequel to Low Cost SET Amp for Newbies

On Tue, 15 Jul 2014 18:58:23 -0600, maxhifi wrote:

Patrick Turner wrote:

John Stewart proposes a low cost SE amp using 6LU8.
http://www.audiobanter.com/attachmen...tachmentid=379

It is many years since that tube has been made. Maybe not everyone
could obtain one. Pentode Pda rating = 14Watts, so say 12W max in
practice for SE class A1. This means max Po = 5 Watts with low OPT
losses, at 42% anode efficiency.

snip


The 6LU8 is all but unobtainable here in the UK. It often costs far more
for the postage than it does for the valve - and we always get hammered
on postage from the US. (The postage is far cheaper from China). 1/2
ECC88 / 6L6 seems to work quite nicely but has a bit less gain than
ECC83/12AX7 for the first stage. The Hammond 125SE OPT also seems to be
quite reasonable for the money - especially when you look at how much it
costs for "proper" iron over here. They are probably on a par with
similarly specified Edcor.
  #10   Report Post  
Posted to rec.audio.tubes
maxhifi maxhifi is offline
external usenet poster
 
Posts: 164
Default Sequel to Low Cost SET Amp for Newbies



mick wrote:

On Tue, 15 Jul 2014 18:58:23 -0600, maxhifi wrote:

Patrick Turner wrote:

John Stewart proposes a low cost SE amp using 6LU8.
http://www.audiobanter.com/attachmen...tachmentid=379

It is many years since that tube has been made. Maybe not everyone
could obtain one. Pentode Pda rating = 14Watts, so say 12W max in
practice for SE class A1. This means max Po = 5 Watts with low OPT
losses, at 42% anode efficiency.

snip

The 6LU8 is all but unobtainable here in the UK. It often costs far more
for the postage than it does for the valve - and we always get hammered
on postage from the US. (The postage is far cheaper from China). 1/2
ECC88 / 6L6 seems to work quite nicely but has a bit less gain than
ECC83/12AX7 for the first stage. The Hammond 125SE OPT also seems to be
quite reasonable for the money - especially when you look at how much it
costs for "proper" iron over here. They are probably on a par with
similarly specified Edcor.


For you guys in the UK how about a PCL86 based version of the amplifier?
Should be able to find some cheap NOS over there, and it even uses a more
conventioal tube socket.



  #11   Report Post  
Posted to rec.audio.tubes
maxhifi maxhifi is offline
external usenet poster
 
Posts: 164
Default Sequel to Low Cost SET Amp for Newbies



maxhifi wrote:

mick wrote:

On Tue, 15 Jul 2014 18:58:23 -0600, maxhifi wrote:

Patrick Turner wrote:

John Stewart proposes a low cost SE amp using 6LU8.
http://www.audiobanter.com/attachmen...tachmentid=379

It is many years since that tube has been made. Maybe not everyone
could obtain one. Pentode Pda rating = 14Watts, so say 12W max in
practice for SE class A1. This means max Po = 5 Watts with low OPT
losses, at 42% anode efficiency.

snip

The 6LU8 is all but unobtainable here in the UK. It often costs far more
for the postage than it does for the valve - and we always get hammered
on postage from the US. (The postage is far cheaper from China). 1/2
ECC88 / 6L6 seems to work quite nicely but has a bit less gain than
ECC83/12AX7 for the first stage. The Hammond 125SE OPT also seems to be
quite reasonable for the money - especially when you look at how much it
costs for "proper" iron over here. They are probably on a par with
similarly specified Edcor.


For you guys in the UK how about a PCL86 based version of the amplifier?
Should be able to find some cheap NOS over there, and it even uses a more
conventioal tube socket.


Also, Radio Spares has an oputput transformer I would use for this design if I
was a UK citizen... http://uk.rs-online.com/web/p/audio-...rmers/2106475/
That with an adapted circuit for a PCL86 would be a good start.

Reply
Thread Tools
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Low Cost SET Amp for Newbies John L Stewart Vacuum Tubes 1 January 8th 14 04:09 PM
Sequel II cleaning [email protected] Pro Audio 1 August 16th 07 10:36 PM
old farts only (the sequel) Bob Pro Audio 0 October 4th 04 07:39 AM
Studio wiring advice for newbies by newbies Steve Jorgensen Pro Audio 24 June 29th 04 02:29 AM
Studio wiring advice for newbies by newbies Steve Jorgensen Pro Audio 0 June 25th 04 09:23 AM


All times are GMT +1. The time now is 10:40 AM.

Powered by: vBulletin
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 AudioBanter.com.
The comments are property of their posters.
 

About Us

"It's about Audio and hi-fi"