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Re: Make that "Darren: (sp)

4/5/2005 8:12 PM
Greg SimonRe: Make that "Darren: (sp)
On the wiring on this Silvertone, I used Mogami 2330 shielded cable into and out of all gain stages, and to and from the tone stack due to necessity, as they have the tone controls outside and on top of the chassis. The amp is possibly the worst laid out amp I've ever seen, but it seems to be rather quiet except for some hum out of the reverb circuit. I'll get to that part later though...still getting the gain dialed in! I completely changed the layout of the preamp stages and wire routing, and planned it out on paper before doing it to make it work well with the increased gain, and even with that, I had to gut it again and redo the grounding scheme when I had too much hum.  
 
Mark, I had TONS of squeal before I reduced the number of gain stages. What is your supply voltage to the pentode? In this one it is somewhere around 330v I think....I'll have to measure again. Won't get a chance until tomorrow. The plate voltage on the pentode was around 120v I think.  
 
The tone stack is a blackface stack, but with some different values as I noted in the other post. After I get the voltages where I want them, I may tweak the tone stack a bit to see how the sound changes, but so far it sounds pretty good, and NO squeal! The EF86 > CF > tone stack > volume control > 1/2 12au7 gain stage seems to work well, with the tone stack dropping a bit of gain. I heard it is one of the more lossy ones so that is why I chose it. The CF is there to maximize gain of the EF86 and to isolate it from the load of whatever follows it, and I like the sound of a tone stack preceded by a CF too. It definitly has too much gain with a 12ax7 or 12ay7 in place of the 12au7. I'm going to see if I can warm up the 12au7 stage though, because the plate voltage drops to 49v with it in there whereas the 12ax7 was around 140v, and I don't want a ton of cutoff distortion out of that stage...I'm just looking for a smooth, warm gain to reinforce what the pentode is doing. I'll be able to post more tomorrow.  
Greg