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  #1  
Old April 22nd 17, 09:05 AM posted to rec.audio.tubes
Frank Lucas[_2_]
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Posts: 2
Default GZ34

So I've decided to buy two brand new JJ's GZ34 for my two mono 2A3 amps.
JJ's are cheap and I thought that if they were to last a few months
before selling the amps they were good enough.
I replaced the old chinese Golden Dragons (5AR4) and everything worked
flawlessly. The sound was a bit thin but I thought it was just matter of
waiting a few days for the tubes to express themselves better.
Then when I was going to leave everything as it was and replace the amps
with the love of my life the Dynaco ST35 ...

A friend stopped by with a bag of old Mullards GZ34 to put in those amps
and the something really strange happened.

I always prefer double blind testing, I'm an atheist, I don't believe in
cable magic or snake oil or in Bolduc's mystical runes and I trust my
ears more than my eyes.

The difference between the sound with the JJ's and the one with the
Mullards is so clear that even being in another room you could feel the
change. Dynamics, bass response, sweetness ... I was stunned.

The difference when we tried to swap the humble Guiguang monoplate 2A3Bs
with the pricey AVVTs was almost inexistent apart from the latter being
too metallic and so the worst of the two. Great difference was achieved
instead when we tried a couple of Marconis NOS.

Further investigation with the use of a scope and a signal generator
showed that with the Mullards the sag was less and recovery was faster.

Would a couple of solid state rectifiers with a properly calculated
series resistances and maybe a standby switch act better than the mighty
Mullards?

The 35 is still on a shelf waiting ...

Are there any brand of GZ34 or 5AR4 that resemble the sound of the
Mullards or in other words that act electronically like Mullards?

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  #2  
Old April 22nd 17, 03:47 PM posted to rec.audio.tubes
martin
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Posts: 1
Default GZ34

On 2017-04-22, Frank Lucas > wrote:
> So I've decided to buy two brand new JJ's GZ34 for my two mono 2A3 amps.
> JJ's are cheap and I thought that if they were to last a few months
> before selling the amps they were good enough.
> I replaced the old chinese Golden Dragons (5AR4) and everything worked
> flawlessly. The sound was a bit thin but I thought it was just matter of
> waiting a few days for the tubes to express themselves better.
> Then when I was going to leave everything as it was and replace the amps
> with the love of my life the Dynaco ST35 ...
>
> A friend stopped by with a bag of old Mullards GZ34 to put in those amps
> and the something really strange happened.
>
> I always prefer double blind testing, I'm an atheist, I don't believe in
> cable magic or snake oil or in Bolduc's mystical runes and I trust my
> ears more than my eyes.
>
> The difference between the sound with the JJ's and the one with the
> Mullards is so clear that even being in another room you could feel the
> change. Dynamics, bass response, sweetness ... I was stunned.
>
> The difference when we tried to swap the humble Guiguang monoplate 2A3Bs
> with the pricey AVVTs was almost inexistent apart from the latter being
> too metallic and so the worst of the two. Great difference was achieved
> instead when we tried a couple of Marconis NOS.
>
> Further investigation with the use of a scope and a signal generator
> showed that with the Mullards the sag was less and recovery was faster.
>
> Would a couple of solid state rectifiers with a properly calculated
> series resistances and maybe a standby switch act better than the mighty
> Mullards?
>
> The 35 is still on a shelf waiting ...
>
> Are there any brand of GZ34 or 5AR4 that resemble the sound of the
> Mullards or in other words that act electronically like Mullards?
>

I cant answer that question but I am interested because in the 60's
in fact from 65 to 71 I worked in the Mullard stores in Mitcham
where lorryloads of valves used to come in unmarked, apart from
a datecode round the base, which i dont remember any more, we always
knew they were the best. THe only equivalents in those days were
Russian valves, which were used in some marine equipment.
I has been interesting reading these threads, and i still have a
copy of Radio Valve Data from 1961.

--
Martin

  #3  
Old April 23rd 17, 10:46 PM posted to rec.audio.tubes
Peter Wieck
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Posts: 2,414
Default GZ34

The answer is pretty basic as you found:

Modern off-shore 5AR4s are crap. They will not pass enough clean DC current for the amp(s) to operate properly.

There are after-market solid-state 5AR4s which are adequate, far better than the Chinese/Russian garbage. Search for "WEBER COPPER CAP", and you will find the one with the best reputation *and* a built-in delay.

And there are delay boards (15 seconds is suggested) that may be had as well. Neither of these devices likes short-cycling, so do understand that before investing in them.

The most common mod on the Weber is to remove the cover, ventilate it, and then put it back. They get HOT!

Peter Wieck
Melrose Park, PA


  #4  
Old April 25th 17, 10:48 PM posted to rec.audio.tubes
Frank Lucas[_2_]
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Posts: 2
Default GZ34

On 23/04/2017 23:46, Peter Wieck wrote:
> The answer is pretty basic as you found:
>
> Modern off-shore 5AR4s are crap. They will not pass enough clean DC current for the amp(s) to operate properly.
>
> There are after-market solid-state 5AR4s which are adequate, far better than the Chinese/Russian garbage. Search for "WEBER COPPER CAP", and you will find the one with the best reputation *and* a built-in delay.
>
> And there are delay boards (15 seconds is suggested) that may be had as well. Neither of these devices likes short-cycling, so do understand that before investing in them.
>
> The most common mod on the Weber is to remove the cover, ventilate it, and then put it back. They get HOT!
>
> Peter Wieck
> Melrose Park, PA
>
>


I've read lot of positive reviews about Matsu****a nos 5ar4/gz34 made
using Mullard machines. Maybe I'll try them one of these days.
I'd like to build some solid state rectifiers using some resistor to
simulate the voltage drop typical of a tube rectifier to leave the amp
circuit untouched in the bias voltage section but I'd also like to build
them with some kind of soft start to avoid the standby switch.
I really want to know what's inside those Webers ...

Frank
Florence, Italy
  #5  
Old April 26th 17, 01:15 PM posted to rec.audio.tubes
Peter Wieck
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Posts: 2,414
Default GZ34

On Tuesday, April 25, 2017 at 5:48:52 PM UTC-4, Frank Lucas wrote:
> On 23/04/2017 23:46, Peter Wieck wrote:


> I really want to know what's inside those Webers ...
>
> Frank
> Florence, Italy


http://www.tdpri.com/threads/solid-s...estion.182474/

Here it is. They do work, reasonably well.

Peter Wieck
Melrose Park, ,PA

  #6  
Old July 25th 17, 08:55 AM posted to rec.audio.tubes
Big Bad Bob
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Posts: 323
Default GZ34

On 04/26/17 05:15, Peter Wieck wrote:
> On Tuesday, April 25, 2017 at 5:48:52 PM UTC-4, Frank Lucas wrote:
>> On 23/04/2017 23:46, Peter Wieck wrote:

>
>> I really want to know what's inside those Webers ...
>>
>> Frank
>> Florence, Italy

>
> http://www.tdpri.com/threads/solid-s...estion.182474/
>
> Here it is. They do work, reasonably well.


I expect a simple series resistor does the trick, but an actual tube's
behavior might be nonlinear...
  #7  
Old July 25th 17, 01:27 PM posted to rec.audio.tubes
Peter Wieck
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Posts: 2,414
Default GZ34

On Tuesday, July 25, 2017 at 3:55:33 AM UTC-4, Big Bad Bob wrote:

> I expect a simple series resistor does the trick, but an actual tube's
> behavior might be nonlinear...


Yes. The 5AR4/GZ34 and related clones are a (relatively) slow-onset rectifier that (theoretically) allows the output tubes to get hot before seeing B+. This, thereby, reduces the strain on the filter caps.

The Weber "copper top" et.al. solid-state replacements are not quite as slow, but neither are they as expensive as a decent 5AR4, and also should last longer.

Peter Wieck
Melrose Park, PA

  #8  
Old July 28th 17, 02:16 AM posted to rec.audio.tubes
[email protected]
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Posts: 13
Default GZ34

I've done both, home grown in Amphenol octal plugs & bought some from New Sensor. All worked OK as long as the power tubes were OK with the higher HV. Some of the power tubes manufactured after the glory daze of toobs did not like it at all, as others have seen.

Growing your own it is possible to insert different value resistors in series with each diode in order to equalize the charging current into the PS filter.
The PS transformer is wound serially so that the two sides of the winding are not the same resistance.

That way it is possible to minimize or even eliminate the power frequency (60 Hz in NA, 50 Hz in Europe)component in the ripple. That is important in SE triode amps, 2/3 to 4/5 of all the PS ripple is delivered to the speaker.. Might be at a resonance. The LC PS filter often used is 12 db less effective at the power frequency than at the regular ripple frequency.

Cheers to all, John L Stewart

  #9  
Old July 31st 17, 09:00 PM posted to rec.audio.tubes
Big Bad Bob
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Posts: 323
Default GZ34

On 07/27/17 18:16, wrote:
> The PS transformer is wound serially so that the two sides of the winding are not the same resistance.


I'm not sure how having a tube rectifier there, vs solid state, would in
any way improve the hum factor.

As for the PS transformer, they were obviously being cheap if that happens.


one appeal of tube vs solid state rectifiers is the 'punch' effect you
get with a guitar amp. At high load you get an 'attack/decay' amplitude
effect because the capacitors discharge for a short time, giving you
slightly higher power levels than the power supply can deliver with a
sustained signal. This is due to internal resistance of the rectifier
tube. But if the behavior is non-linear, having a series resistor on a
diode won't give you the same effect...

Anyway, they should be using LC filters after the diode to minimize hum,
and a properly balanced power transformer secondary winding. That's how
the old Hi Fi systems were done. Just boost secondary voltage a bit to
compensate...

/me would consider adding a series voltage regulator using a transistor
and zeners and solid state rectifiers and a current limiting circuit, to
give you a nice clean primary power supply that doesn't 'surge' the
capacitors when it starts up. A 25-50V drop would be sufficient, not
unlike what you get with a tube rectifier anyway.

but yeah, that's not very 'purist' of me. I just think the pre-amp and
output tubes are what matters for hifi tube audio, or guitar amp audio
for that matter. The power supply [other than the 'punch' effect] is
less important, but could be simulated if needed, using a derivative of
a current limiter circuit.

  #10  
Old August 4th 17, 05:39 PM posted to rec.audio.tubes
[email protected]
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Posts: 13
Default GZ34

The PS transformer is wound serially so that the two sides of the winding are not the same resistance.

I did the work on this all of 20 years ago. The results got published in Glass Audio Volume 10, Number 3, 1998 & Electronics World (June 1998). And posted on RAT, several times over several years. I’m surprised you are unaware of it. The resulting problem applies only to SET amplifiers, although PS hum sidebands do show up on the output off PP amps. Measured & posted that too.

The simple, low cost fix reduces the power frequency (60 Hz)hum component as much as 20 db. A simpler fix reverses the HV leads to the rectifier. That way for a filamentary rectifier such as the common 5U4G one of the HV wdg will be in series aiding while the other is series opposing to the 5V across the cathode surface. That is enough to yield a 15 db reduction in the power frequency component. And costs us nothing. Half of the amps built probably have those leads hooked up wrong way around.

Better measure some of your power transformer HV windings carefully. That is easy these daze with a digital meter. If you find any where the halves are the secondary are the same resistance, post the p/n & manufacturer here. Any I’ve ever looked at were in all cases different resistance.
Most of the schematics show resistance for the halves of the secondary to be the same. But they are not. Quite a few of the old radio schematics out of the 30’s show the actual HV resistances. For example, the Philco 37-93 is given as 230R & 250R.

I'm not sure how having a tube rectifier there, vs solid state, would in
any way improve the hum factor.

But there is a difference. The forward resistance of a SS diode is much less than a Toob. So the charging currents are larger, if all other things are left the same. The there is more hum resulting. Much of the work on that was done in the 30s by Terman & others, all in his textbooks. And copied into the Radiotron Designers Handbook (RDH4), commonly used by many of us old guys. All easy reading.

As for the PS transformer, they were obviously being cheap if that happens.

Not cheap at all, simply makes good business sense. Over many years in sales with HP & R&S I had quite a bit of contact with Hammond. One comment I recall had to do with the relative cost of a tap vs. starting another winding.. By the time that extra step filters thru to the end user it could be significant. Sales volume depends on reasonable cost as well as perfection.

one appeal of tube vs solid state rectifiers is the 'punch' effect you
get with a guitar amp. At high load you get an 'attack/decay' amplitude
effect because the capacitors discharge for a short time, giving you
slightly higher power levels than the power supply can deliver with a
sustained signal. This is due to internal resistance of the rectifier
tube. But if the behavior is non-linear, having a series resistor on a
diode won't give you the same effect...

Anyway, they should be using LC filters after the diode to minimize hum,
and a properly balanced power transformer secondary winding. That's how
the old Hi Fi systems were done. Just boost secondary voltage a bit to
compensate...

/me would consider adding a series voltage regulator using a transistor
and zeners and solid state rectifiers and a current limiting circuit, to
give you a nice clean primary power supply that doesn't 'surge' the
capacitors when it starts up.

SS circuitry makes life easy in many ways, so SS regulation is a possibility. Not so much when Williamson & the others got going.

A 25-50V drop would be sufficient, not
unlike what you get with a tube rectifier anyway.

but yeah, that's not very 'purist' of me. I just think the pre-amp and
output tubes are what matters for hifi tube audio, or guitar amp audio
for that matter. The power supply [other than the 'punch' effect] is
less important, but could be simulated if needed, using a derivative of
a current limiter circuit.

The guitar pickers & other electronic musicians have much greater problems to solve than PS hum. Ground loops can be a killer. It is somewhat of a surprise that we don’t see a lot more balanced systems as used in broadcast where 600 ohms transformers are used. There certainly have the audio bandwidth required. But here again cost is a killer.

This note is not meant to flame you or anyone else. Just some information where I’ve had a careful look at a potential problem & found a reasonable way out!
 




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