Dumble Bargain

[ijedouglas]

Anyone notice the larger (3A?) diode in the bias circuit? I wonder if that was done for tone? I know there has been a discussion regarding diode type (fast/soft...) having an impact on the tone.

[martin manning]

Most people believe solid-state rectifiers sound different from vacuum, but in cases where solid state and vacuum are compared in the same amp, the difference is has been found to be minimal if anode voltage and bias setting are controlled. Differences between solid state rectifiers of the same type (or current rating in the same type) are likely to be extremely small, and in the case of push-pull output sections will tend to be cancelled in the output transformer. I don't see debate around solid state rectifiers in a quick search, other than the noise reduction potential of fast recovery diodes.

[ijedouglas]

So if there is no impact to the tone/sound/feel of the amp, why would he have put a different diode in that position?

[martin manning]

Who knows? Why use a high current diode in a low current (bias supply) application? Some Hi-Fi types have claimed different brands of tube rectifiers have different sound, but I'm not aware of any such claims around high-current solid state rectifiers.

[ijedouglas]

I would love to know. I have not heard a difference between 3A and 1A diodes but I can definitely hear a difference between standard (1N4007) and fast recovery diodes. I can also hear a difference in the resistors in the bias circuit so maybe HAD could hear/feel something with that diode. I highly doubt he would just randomly use a larger diode in that position.

I happened to be watching this and it piqued my interest:

[martin manning]

What part of the 1:32:24 was it that piqued your interest?

[ijedouglas]

The 3A diode in the bias supply

[talbany]

I would love to know. I have not heard a difference between 3A and 1A diodes but I can definitely hear a difference between standard (1N4007) and fast recovery diodes. I can also hear a difference in the resistors in the bias circuit so maybe HAD could hear/feel something with that diode. I highly doubt he would just randomly use a larger diode in that position.

I happened to be watching this and it piqued my interest:

The video is disabled??
Dumble also used this diode STK-9010 1000V 3A in the Silver Alligator in the mains bank and 1N4007's in the bias?

6A6699C7-1C8B-46F8-B8CA-846D1D9CE008.png

This is what I've found on FRED's
https://ampgarage.com/forum/viewtopic.p ... es#p408589

Tony

[ijedouglas]

The video is disabled??

Yeah, just click on it and it will take you to YouTube.

I think the link you provided that was the discussion I was referring to. Any idea why he would use a 3A over a 1A when they are both way over spec'd for the job at hand?

[talbany]

Any idea why he would use a 3A over a 1A when they are both way over spec'd for the job at hand?

No

[martin manning]

The 3A diode in the bias supply

I thought you meant there was something specific about rectifiers in that YouTube that drew your attention to the bias diode.

Any idea why he would use a 3A over a 1A when they are both way over spec'd for the job at hand?

No

HAD seems to have used replacement parts that were available from local electronics shops, or possibly from surplus shops. Maybe it was just something he had lying around, and he put it in that important location thinking that it would probably never fail?

Fast recovery diodes are required for high-speed operation in SMPS, typically 500-1000x higher than the 60-120Hz in a linear power supply. No reason not to use them at low frequency in pursuit of noise reduction, unless you are a volume manufacturer trying to pinch pennies. Here is a trace showing the reverse-bias switching transient: https://ampgarage.com/forum/viewtopic.p ... 6&p=187281 At low current, the reverse flow isn't visible at all at 100 Hz, very obvious at 10 kHz.

[Max]

... (Caps say 1976) ... I was dating the amp (using the most recent cap date as a reference) ...

" ... FULL RIVER CAP.CO.,LTD (MIEC) was established in 1979, more than 40 years experiences in this area, we specialize in producing aluminum electronic capacitor, major products are middle and high voltage capacitor, MIEC is able to provide fast, flexible and innovative approaches to meet the needs of the market. ..." https://www.miec-cap.com/index/index.php

[ijedouglas]

... (Caps say 1976) ... I was dating the amp (using the most recent cap date as a reference) ...

" ... FULL RIVER CAP.CO.,LTD (MIEC) was established in 1979, more than 40 years experiences in this area, we specialize in producing aluminum electronic capacitor, major products are middle and high voltage capacitor, MIEC is able to provide fast, flexible and innovative approaches to meet the needs of the market. ..." https://www.miec-cap.com/index/index.php

Based on the listing description, the amp was brought back to HAD after he bought it in 1988 to have the tremolo circuit installed. HAD also seemed to use the MIEC caps in later (5th gen on) amps. I don't think we should be trying to date the amp based on those MIEC caps The TVAs do seem to be original though.

[Max]

And what exactly do you mean by "original" in this context?

[ijedouglas]

And what exactly do you mean by "original"?

"original" would mean originally installed in the amp when it was built. Pure conjecture but a good chance don't ya think?