1n4007 posts

[Dustoff]

Hi all!
New here, been reading and researching alot. Mainly because I am heading into a couple of express builds, first time, but not completely void of knowledge, but not an expert. I have read a few posts on the tonal effects from the 1n4007 diodes. I thought id throw this out there and see of anyone has tried this: i am a ham radio operator, builder etc. and when i build rectifiers for RF amplifiers, whether home brewed or retail built, its common practice to place a .01 uf 1KV ceramic cap across each diode to remove the "switching" noise. I don't know a lot about effecting tone, but has anyone tried this? Just had to ask, lots of knowledge here, i commend all of you for the help and information that is given here, incredible!

Mike

[Blackburn]

Hey Mike,

That's a Dumble thing and not a Wreck thing. I would say you probably won't need to do this if you're building Expresses. Check out the Dumble files and pics for more detail on the subject. Ken used two 100K 3W bleeder resistors to discharge the fully charged cap on the hot side of the rect and also provides noiseless switching.

David

[martin manning]

As I recall the discussion on the TW side is around the tonal effect of the 3x1N4007 reverse-biased diodes on the power tube sockets.

[Blackburn]

Oh yeah, sorry. I immediately thought of the rectumfrier, where I've seen those .01s.

[BTF]

You see that scheme as well on some of the Rivera-era Fenders.

I tried paralleling .01uF caps with 4007s on some early preamp builds I did in the early 80's. I honestly could tell no benefit or detriment. My intention was less to prevent switching noise, but the idea that it might reduce line noise from multiple devices plugged into rack power strips. I still place .01uF caps across the outputs of bridge rectifiers and across the outputs of bridge and full-wave rectifiers I use for remote pedalboard supplies.

At RF frequencies, the reduction in switching noise might probably affect the operation of the unit. In my experiments with preamps- both electric and acoustic- I can't really say I can tell a difference, but I do it anyway.

No help, I know. Regards, Bill.

[Dustoff]

I guess i should have stated the use at the tubes, the rectifier was the reference to controlling some of the switching noise. Lots to learn, probably why i still read, research and constantly experiment!

Mike

[tonewood]

Here is an example of reducing potential switching noise using caps.

http://www.valvewizard.co.uk/bridge.html

[BTF]

My apologies! I thought you were asking about rectifier caps.

I've never used caps at the plates for suppression of flyback voltage.

[Ang3lus]

what about using UF4007 didoes instead ?

[overtone]

Here is a excerpt from the Trainwreck Pages by Ken Fisher.
The last sentence from KF is a key.
He does not use the word flyback, which is often put forward as the reason for this modification. That discussion opens a can of worms about how to best protect amps if you loose the speaker load etc.

To my mind KF was concerned about spike suppression, so isn't the application here parallel negative clippers applied to clamp each side a PP output stage when driven to clipping?

I don't see a case for caps across the diodes in this application, but stand to be corrected.

Best, tony

[Diablo1]

The series diodes on pin 3 to ground of the output tubes is from the Ampeg V4 of around 1971. KF worked for Ampeg, so it looks like he borrowed the idea for his Trainwreck, not that there's anything wrong with that.

[martin manning]

Seems like two conversations are going on here. I believe the original question was referring to the "flyback" diodes from plate to ground on the power tubes. In the excerpt from the TW pages posted by Tony above KF specifically says he doesn't use high-speed diodes because they will alter the tone, and I assume he means not in a good way. As i recall there were a couple of reports of strange artifacts that disappeared when these diodes were removed. They were included on some Ampegs as Diabolo1 says, as well as on some other brands. Ampeg later dropped the diodes, and used some other tricks to prevent damage from running without a load. I can only imagine that they had too many cases where this occured, and wanted to reduce the occurrences and expese of dealing with them.

[Structo]

You're right Martin I was confused as well.