I wonder how many of you hear what these do to your audio as you play? Eh, but maybe it's just me. As you hit the amp pretty hard, there's a kind of weird almost oscillation type thing that happens, like you've got a bad power supply cap.
One time Glenn talked about this sound in his amps. Glenn? I am just sending this out to any who have maybe heard that weird sound. Today I disconnected the diodes and that sound went away. I won't be putting them back in.
If I lose a PT or an OT, so be it, although I really doubt this will ever happen. Frankly, hearing the amp the way it sounds right now, I feel like I want all those years back that I lost, keeping the circuit stock. What a waste of a great guitar tone. YMMV!
Most people stall out when fixing a mistake that they've made. Why?
It's a sort of deep confused hesitation/distortion that overwhelms the main note; like a low pitched ghost note that tries to take over the true note. You might think your PI is acting up or a power tube is failing almost. That or a power cap is failing.
As you play, its not a 24/7 type thing, but a kind of build up and release almost. It's more noticeable as you dig in to play double stops, for example, and, if you just coast along picking lightly you may never hear it.
Most people stall out when fixing a mistake that they've made. Why?
If you're referring to the fly-back diodes, I also had a problem with them installed on my amp. Mainly at higher volumes and hard pick attack, I would get a static kind of sound trailing the note. At first I didn't know what was causing the nasty sound, but I was rewiring the power tube sockets and fired it up without them installed and the noise was gone. Just to make sure I re-installed them and the noise was back... I check the polarity of the diodes to make sure they were right... I can't explain why my Express does this and others don't, but I also got no viable explanation from anyone in the group, so I left them off...
I have heard that "trailing static" , but not the OP's noise description. Maybe I'll try lifting one side of the diode strings to see (when I get my amp back from a friend I loaned it to).
sliberty wrote:I have heard that "trailing static" , but not the OP's noise description. Maybe I'll try lifting one side of the diode strings to see (when I get my amp back from a friend I loaned it to).
Just out of curiosity, does your Express have external bias points?
I also ran into a post where someone was talking about Ken Fischer, about how he said the 'diode string' didn't work in every circuit. Whether he said this or not, it gave me pause for thought. I have a BFSR here that I had installed these on and, oddly enough, it exhibited the same type of behavior although I hadn't put the two together. I removed it from the SR and the effect went away. Hm. Funny thing, although in hindsight the two amps were exhibiting the same issue, it took me a while to consider that the Express circuit was doing this as well. And here I think it's because I was just assuming that the Express circuit was Ken Fischer designed and couldn't be flawed. And, like you say, sliberty, as far as you are concerned the Express you have doesn't exhibit this thing that I describe - I felt that way too. Ha! Really, I did. But when I removed the two diode strings and played the amps (2), that weird sound that I describe was gone. The amps were immediately improved.
As to the 'static kind of sound', Randy, well, OK, I can't use that word because to me the word 'static' implies a kind of surface noise and the sound I heard is somewhat deep in the bowels of the amp. But I'm sure we are both reporting the same event, it's maybe ears and our particular perceptions that cause us to express things differently.
To be logical here, the intent of the string of diodes, properly called the 'Transient suppression mod' (actually 1/2 of it, the other being the varistor placed on the PT primary) published in 1986 (and probably in Vintage Guitar magazine prior to that) in the Groove Tubes book, The Tube Amp Book, was to afford some protection to the power tubes. That is the only written explanation by Ken. It does not say they will protect the PT or the OT. And I point this out because I think some people equate this mod with the means of protecting the amp from all kinds of goblins. (Well, that is if they are into it. Many are not.) At any rate, when you think about it, just as Ken's description states it will, 'reduce the transient spikes that eat up power tubes usually present when the amp is really cranked way up.', this is the point at which you would hear the effect of the diodes. If you don't turn it up you will never hear the effect, although I do agree that, in a perfect world, the effect should never be heard at all. And I also should use the word 'feel' here because a lot of my complaint is that the 'feel' of the bloom was ruined by the diode circuit - it is something someone not playing the guitar might ever notice as they listen.
Getting back to Glen, I wish he would chime in here. Since he owns an original Express, and cranks it regularly, he could speak to this. Or not.
Most people stall out when fixing a mistake that they've made. Why?
rooster wrote:Ha, mine are are 1N4007s. From what I read this is what Ken suggested. What's up, Colossal?
Oh nothin', was just wondering as I recall reading one of Ken's aversions was to ultra-fast recovery diodes. I didn't think you had them in your amp but figured I'd ask on chance you might.
ken worked at ampeg for a while. ampeg put the diode string in their bigger amps in the 70's. they thought it was a good idea and he probably did as well, since i'm sure he probably learned a good bit while working there. rh
rooster wrote:Ha, mine are are 1N4007s. From what I read this is what Ken suggested. What's up, Colossal?
Oh nothin', was just wondering as I recall reading one of Ken's aversions was to ultra-fast recovery diodes. I didn't think you had them in your amp but figured I'd ask on chance you might.
Interesting, I have UF4007s in my express. I have had what may be similar behavior to the OP, once again, mostly when played hard. I may swap for 1n4007s, or remove the string for comparison.
It might be interesting to bypass the diode string with an 0.1uF high voltage film cap or ceramics to shunt any switching noise to ground (assuming switching noise is actually what this behavior that you guys are observing is). It might not be a good solution tonally but would at least put the idea to the test.
Instead of a diode string to ground on each output tube plate, RG Keen suggests using a 600V 60J MOV across each plate lead/OT primary and B+1.
