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Old 5th Oct 2022, 6:09 pm   #21
G.Castle
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Default Re: GZ37 rectifier and the Wadar amp

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Originally Posted by Ian - G4JQT
Most hi-fi amps use silicon diodes in the power supplies so I don't understand the problem, or are the reservations regarding mixing silicon and thermionic rectifiers?
I don't understand the problem either, leaving the valve rectification as well as having the silicon in series tends to negate the problem of over volting the reservoir capacitor, the valve acting as a surge limiter: at least from switch on from cold. The tendancy for the HT to have sag with the valve still there will remain, your choice to believe this being a good or bad thing for your application.

As for the capacitors around the S/S diodes, I'd still prefer to put a fast rectifier in there rather than the 1N400* series.

Greg.
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Old 5th Oct 2022, 8:59 pm   #22
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Default Re: GZ37 rectifier and the Wadar amp

Thanks G. Castle. There's some interesting info in that thread that I missed.
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Old 6th Oct 2022, 2:47 pm   #23
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Default Re: GZ37 rectifier and the Wadar amp

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Therefore I'm minded to add 1N4007 diodes in series with each of the rectifier anodes as shown in post #5 with a replacement GZ34, although some posts here advise against this.

Nevertheless, if I add these diodes is there any benefit in putting say 0.01 uF disc ceramic capacitors in parallel with each diode, or from diode cathodes to earth, or between cathodes as there is some reservation regarding adding silicon diodes. Most hi-fi amps use silicon diodes in the power supplies so I don't understand the problem, or are the reservations regarding mixing silicon and thermionic rectifiers?
The valve diode controls the rectified current pulse turn-off, allowing it to be benign with respect to generating an L.di/dt transient from the power transformer leakage inductance. Using a 1N4007 or UF4007 in series makes no difference to the turn-off characteristic. The 1N4007 has the benefit of a higher actual PIV (circa 1.5kV), and a lower leakage current, than the UF4007.

Power supplies for low voltage high current ss amplifiers cause a much more onerous turn-off transition with the rectifier diodes, making the ss diode reverse recovery characteristic become noticeable.
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Old 6th Oct 2022, 5:02 pm   #24
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Default Re: GZ37 rectifier and the Wadar amp

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The 1N4007 has the benefit of a higher actual PIV (circa 1.5kV), and a lower leakage current, than the UF4007.
They're both rated at 1,000V PIV! Though you may be lucky and have some which in practice can withstand more.

Agree about leakage current - the dopants which give fast recovery, work by creating recombination centres to neutralise stored charge. And unfortunately they also act to give more leakage current.
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Old 7th Oct 2022, 12:00 am   #25
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Default Re: GZ37 rectifier and the Wadar amp

There are many who have measured the actual PIV of their 1N4007, and even 1N4004 have been measured as the same. The topic of modern day manufacture was one reason for peoples interest, as it made no commercial sense to batch manufacture specifically for the 1N400x variants, especially from 1N4004 upwards.

My batch of 1N4004 achieve better than circa 1.4kV. Sure, not all manufacturers are the same given the generic part, but if you have a batch from a reputed manufacturer and can do a quick test (as a few have done), then for 'back-up' applications like using them in series with a valve diode it can be a benefit, with the caveat that if the valve is operating in an application needed a PIV above 1kV (eg. above circa 300-0-300V secondary given tolerances) then at least 2x 1N4007 in series are preferred.
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Old 7th Oct 2022, 9:06 am   #26
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Default Re: GZ37 rectifier and the Wadar amp

Hello Ian,

Am I right in assuming you wrote ‘At Last I built a Wadar amplifier’ in the Autumn 2019 edition of the BVWS Bulletin? If so, it was a nice article and I made reference to that article in my Article on the Haverson amplifier in the Spring 2022 Bulletin.

Gerrys amplifier is not dissimilar to the basic design used in the Rogers Cadet and the GEC 9-10 making as near a hi-fi amplifier as Gerry would have been comfortable with.

Anyway, a bit of tangential rambling… A good while back I briefly experimented with putting BY133 in series with PY33 to ‘make’ a high voltage hybrid silicon/valve rectifier with a mains transformer secondary voltage of 350-0-350V using a cheaper valve rectifier. I abandoned this quite quickly as I felt it generated too many problems for my own liking especially with PY33 heater voltage. I was concerned about the balance of the voltage across the valve and diode seeing the PY33 has a Va (RMS) max voltage of 250V and the transformer voltage and because of this I considered the two balancing resistors.

Pic attached.

Regards
Terry
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Old 7th Oct 2022, 9:25 am   #27
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Default Re: GZ37 rectifier and the Wadar amp

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Hello Ian,

Am I right in assuming you wrote ‘At Last I built a Wadar amplifier’ in the Autumn 2019 edition of the BVWS Bulletin? If so, it was a nice article and I made reference to that article in my Article on the Haverson amplifier in the Spring 2022 Bulletin.
Hi Terry, yes, that was me. Thank you.

Unfortunately I did make an error on the circuit. I labelled V1 6J7 when is should have been labelled 6SJ7!

Regards,

Ian
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Old 7th Oct 2022, 9:31 am   #28
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Default Re: GZ37 rectifier and the Wadar amp

If there is space on the chassis and you are up to a bit of modification, you could always use a pair of 6D22s colour tv boost diodes - cheap, bomb proof and the 6.3V heaters will run off of the 5V supply very well as their heater current consumption for 2 is less that one GZ37, See Eric Barbour's comments.
I use them in my GEC 88/50 amp as I am not, and never have been, a lover of direct heated rectifiers ie 5U4 types and the GZ32-37 valve range are suffering from "audiophoolery"
You will of course need to be careful as 6D22's have a top cap anode so will require suitable protection unless you don't have nosy children.

John
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Old 7th Oct 2022, 9:32 am   #29
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Default Re: GZ37 rectifier and the Wadar amp

Gerry employed any rectifiers he had to hand providing they supplied enough current for the amps demand. I am not a great enthusiast for directly heated rectifiers but as I mentioned earlier I have a U52/5U4G in mine with absolutely no problems. On switch on they are subject to a great strain that can be seen when looking downwards through the anodes when a very short duration blue glow can be seen as the reservoir cap charges. Elderly examples usually fail on switch rather than fade away due to lack of emission.
These amps do sound really nice on record reproduction and CDs. John.
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Old 7th Oct 2022, 9:46 am   #30
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Default Re: GZ37 rectifier and the Wadar amp

Hello Ian,

Thought it was yourself.

As regards the error we all do it – its easily done… You can proofread until the cows come home, but there will be that blooper which will wriggle through the net.

I made the mistake of mixing up the 6J5 triode and 6J7 pentode in the Sterns 8-10 article.

Regards
Terry.

Quote:
Originally Posted by Ian - G4JQT View Post
Quote:
Originally Posted by Valvepower View Post
Hello Ian,

Am I right in assuming you wrote ‘At Last I built a Wadar amplifier’ in the Autumn 2019 edition of the BVWS Bulletin? If so, it was a nice article and I made reference to that article in my Article on the Haverson amplifier in the Spring 2022 Bulletin.
Hi Terry, yes, that was me. Thank you.

Unfortunately I did make an error on the circuit. I labelled V1 6J7 when is should have been labelled 6SJ7!

Regards,

Ian
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Old 7th Oct 2022, 10:23 am   #31
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Default Re: GZ37 rectifier and the Wadar amp

Why not make a full-wave rectifier in silicon, then you can have a generous reservoir capacitor, then use a thermionic rectifier (maybe a full wave one with anodes strapped) as a slow-start device and also a source of droop to warm the cockles of a guitarist's heart?

You no longer have the anode-to-anode pyrotechnics risk from dubiously manufactured valves

Rate the reservoir for off-load HT with the silicon rectifier. Use fast rectifiers for low noise, and have no worries about leakage.

David
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Old 7th Oct 2022, 1:40 pm   #32
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Default Re: GZ37 rectifier and the Wadar amp

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If there is space on the chassis and you are up to a bit of modification, you could always use a pair of 6D22s colour tv boost diodes...

You will of course need to be careful as 6D22's have a top cap anode...
You'll certainly have to be careful, stand back as the HT electrolytics go pop! The top cap is the CATHODE, as it's the electrode which swings around by a couple of kV in the conventional LOP stage!
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Old 7th Oct 2022, 2:14 pm   #33
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Default Re: GZ37 rectifier and the Wadar amp

The U54 is given as an equivalent to the GZ37 in Babani's book, it's max. Ia(peak) rating is much higher than normal, it being 1.5 Amps which is 12 x max. diode current:

https://frank.pocnet.net/sheets/126/u/U54.pdf

Lawrence.
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Old 7th Oct 2022, 4:50 pm   #34
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Default Re: GZ37 rectifier and the Wadar amp

kalee wrote
"The top cap is the CATHODE, as it's the electrode which swings around by a couple of kV in the conventional LOP stage!"
Oops sorry! put it down to senile decay and the like, sticks head in sand!

John
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Old 7th Oct 2022, 9:58 pm   #35
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Default Re: GZ37 rectifier and the Wadar amp

I read with some interest the points made here & elsewhere regarding silicon diodes being responsible for generating noise - I am not at all decrying the statements made, but I find it odd that I have built very many PSU's for various applications over the years including use of the 1N400x series and have never detected a shred of noise...
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