A Audio and hi-fi forum. AudioBanter

Go Back   Home » AudioBanter forum » rec.audio » Vacuum Tubes
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

Tube mono-block amp with SIX 6L6 outut tubes



 
 
Thread Tools Display Modes
  #21  
Old January 1st 19, 04:27 PM posted to sci.electronics.design,rec.audio.tubes
Kevin Aylward[_5_]
external usenet poster
 
Posts: 2
Default Tube mono-block amp with SIX 6L6 outut tubes

"Big Bad Bob" wrote in message
...

On 12/28/18 09:16, bitrex wrote:

> All amps of that scale should have active protection circuitry/monitoring
> of currents, biases, and temperatures via microprocessor to avoid
> potentially catastrophic faults.


>Even briefly overvolt or overcurrent on a typical transistor, and you'll be
>replacing it VERY soon. I made the mistake of designing a circuit that
>operated close to the maximum Vceo (these 60V transistors should be able to
>handle 45-50V right?), and the transistors never lasted long under load
>(replaced 3 times, and 3 blown fuses that were supposed to protect them).
>Replaced with transistors that had twice the Vceo and no problem.


Well... overcurrent on a mosfet output device is usually pretty safe for
quite a while. Second breakdown is the problem with bipolar. Their rating at
high voltage is much lower than their power ratings would imply.

I designed mosfet amp in the early 80s. I tested it by putting in a full
level signal with an output s/c. The only protection was a zener across the
gates to limit the current to the device ratings. I left it cycling with its
90 Deg heatsink thermal cutout for 3 days. No problems.

-- Kevin Aylward
http://www.anasoft.co.uk - SuperSpice
http://www.kevinaylward.co.uk/ee/index.html

Ads
  #22  
Old January 1st 19, 08:00 PM posted to sci.electronics.design,rec.audio.tubes
Tauno Voipio
external usenet poster
 
Posts: 6
Default Tube mono-block amp with SIX 6L6 outut tubes

On 1.1.19 06:39, Tim Williams wrote:
> "Big Bad Bob" > wrote in message
> ...
>> sounds like a gimmick.* Tube plate/cathode currents are just way too
>> small to properly drive a speaker without an impedence matching
>> transformer.
>>

>
> So what, nothing comes out?...
>
> They were definitely below the maximum power point (at clipping), if
> that's more accurately what you meant.
>
> 6AS7/6080, 6S33S and the other regulator tubes have peak cathode current
> in the ballpark of an ampere, so a modest number of tubes offers a
> modest power output, say 20 or 40W, preferably into a higher load like
> 16 ohms.* The efficiency is poor, with more heat dissipated in the
> heaters alone, than delivered to the output.
>
> If you put dozens in parallel, the efficiency keeps going up as you get
> closer to matching, but now your whole system consumes multiple
> kilowatts...
>
> There was also the Philips "SEPP" with a pair of EL86? driving a
> 100s-ohms voice coil at good efficiency, but those speakers are so rare
> that this is practically a unique case.
>
> Tim
>


The final triodes (6080) are special high-current tubes. The amplifier
designer rated the thing at 25 W into a 16 ohm voice-coil speaker.

--

-TV

  #23  
Old January 2nd 19, 12:02 AM posted to sci.electronics.design,rec.audio.tubes
bitrex
external usenet poster
 
Posts: 5
Default Tube mono-block amp with SIX 6L6 outut tubes

On 01/01/2019 10:27 AM, Kevin Aylward wrote:
> "Big Bad Bob"┬* wrote in message
> ...
>
> On 12/28/18 09:16, bitrex wrote:
>
>> All amps of that scale should have active protection
>> circuitry/monitoring of currents, biases, and temperatures via
>> microprocessor to avoid potentially catastrophic faults.

>
>> Even briefly overvolt or overcurrent on a typical transistor, and
>> you'll be replacing it VERY soon.┬* I made the mistake of designing a
>> circuit that operated close to the maximum Vceo (these 60V transistors
>> should be able to handle 45-50V right?), and the transistors never
>> lasted long under load (replaced 3 times, and 3 blown fuses that were
>> supposed to protect them). Replaced with transistors that had twice
>> the Vceo and no problem.

>
> Well... overcurrent on a mosfet output device is usually pretty safe for
> quite a while. Second breakdown is the problem with bipolar. Their
> rating at high voltage is much lower than their power ratings would imply.


Ya, BJT amps tend to have oversized output devices as compared to what
their rated maximum "RMS power" output would imply. 75 watt-rated
devices in 25 watt amps. The problem is risk of second breakdown when
working into reaactive loads, not de-rating BJTs appropriately when
they're handing significant powers into reactive loads common newbie
mistake

> I designed┬* mosfet amp in the early 80s. I tested it by putting in a
> full level signal with an output s/c. The only protection was a zener
> across the gates to limit the current to the device ratings. I left it
> cycling with its 90 Deg heatsink thermal cutout for 3 days. No problems.
>
> -- Kevin Aylward
> http://www.anasoft.co.uk - SuperSpice
> http://www.kevinaylward.co.uk/ee/index.html


  #24  
Old January 2nd 19, 07:16 AM posted to sci.electronics.design,rec.audio.tubes
Tim Williams[_3_]
external usenet poster
 
Posts: 4
Default Tube mono-block amp with SIX 6L6 outut tubes

"Kevin Aylward" > wrote in message
...
> Well... overcurrent on a mosfet output device is usually pretty safe for
> quite a while. Second breakdown is the problem with bipolar. Their rating
> at high voltage is much lower than their power ratings would imply.


Used to be true -- modern MOSFETs are more than current-dense enough to
exhibit 2nd breakdown. I shouldn't actually say modern, because apparently
SuperJunction process has... PTC source connections or something? I haven't
seen one without a square SOA yet I don't think. So by now, it's actually
previous generation that you have to watch out for. I forget if lower
voltage (SJ goes away under ~400V I think it was?) processes are still
prone.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

  #25  
Old January 3rd 19, 10:25 PM posted to sci.electronics.design,rec.audio.tubes
Kevin Aylward[_5_]
external usenet poster
 
Posts: 2
Default Tube mono-block amp with SIX 6L6 outut tubes

>"Tim Williams" wrote in message ...

>"Kevin Aylward" > wrote in message
...
>> Well... overcurrent on a mosfet output device is usually pretty safe for
>> quite a while. Second breakdown is the problem with bipolar. Their rating
>> at high voltage is much lower than their power ratings would imply.


>Used to be true -- modern MOSFETs are more than current-dense enough to
>exhibit 2nd breakdown. I shouldn't actually say modern, because apparently
>SuperJunction process has... PTC source connections or something? I
>haven't seen one without a square SOA yet I don't think. So by now, it's
>actually previous generation that you have to watch out for. I forget if
>lower voltage (SJ goes away under ~400V I think it was?) processes are
>still prone.


Exicon are the audio mosfets of choice today, apparently. They are laterals.

http://www.exicon.info/

They have the usual power limited SOA.

I don't know who actually makes them, but my guess is someone like XFAB.

Standard fab vendors will make any asic for any fabless company, even if the
asic is just the one big transistor!

-- Kevin Aylward
http://www.anasoft.co.uk - SuperSpice
http://www.kevinaylward.co.uk/ee/index.html

  #26  
Old January 3rd 19, 11:54 PM posted to sci.electronics.design,rec.audio.tubes
[email protected]
external usenet poster
 
Posts: 15
Default Tube mono-block amp with SIX 6L6 outut tubes

On Fri, 28 Dec 2018 14:19:50 +0200, Tauno Voipio
> wrote:

>On 28.12.18 10:45, wrote:
>> On Thu, 27 Dec 2018 21:11:35 -0600,
wrote:
>>
>>> I'm not intending on building this, but it's interesting and makes me
>>> wonder if someone could use EIGHT 6L6 tubes, or TEN?
>>> (Of course adding more tubes mean bigger audio output transformers and
>>> heftier power supplies.

>>
>> Tubes may age at different rates, so the characteristics might be
>> quite different after a long time. It might not make sense to replace
>> a single (failed) tube and you may have to replace the whole set of
>> tubes with new tubes preferably from the same manufacturing batch.
>> This can be quite expensive :-)

>
>
>In the 1960's, I made a guitar amplifier with six EL500's. The tubes
>are not characterized for linear use, and they were not matched in
>any way. Each tube had an own cathode resistor, and there was no
>evidence of any overload from unbalanced operation.
>
>The tubes had a tendency of parasitic oscillation, so I added a
>ferrite bead on the control grids and an inductor-resistor parallel
>combination on each plate (for constructions, see nearest ham handbook).


Back in the late 60s early 70s, I had several (self refurbished)
mono-block power amps that used four 6L6 output tubes. I did not even
know about matching those tubes. I just put in any tube marked as a 6L6.
I recall having both the glass (GC) types mixed with the black metal
ones. I always had good sound and lots of power. I do recall that
replacing the metal cased ones with 6L6GC did increase my power though.
But until I could afford new tubes, I used what I had. And even with the
new tubes, I never matched them.

 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

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

Similar Threads
Thread Thread Starter Forum Replies Last Post
FA: Mono Tube Amp w/ 807 tubes, premium UTC LS-6L3 OPT Stephen F. Marsh Marketplace 0 September 29th 05 02:29 PM
FA: Pair of 2A3 Tube Mono Block "Project" Amplifiers Jon Yaeger Marketplace 2 January 9th 05 07:30 AM
FA: Pair of 2A3 Tube Mono Block "Project" Amplifiers Jon Yaeger Vacuum Tubes 2 January 9th 05 07:30 AM
problem with old mac mono block [email protected] Vacuum Tubes 5 October 10th 03 05:08 PM
Jl 500/1 vs. Alpine 500 watt mono block John Car Audio 1 September 27th 03 10:48 PM


All times are GMT +1. The time now is 05:32 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Copyright ę2004-2019 AudioBanter.
The comments are property of their posters.