Clean issues

[lpd]

Hello guys. I recently modge podged an Express circuit into a Traynor Voicemaster head. Lots of room for the build but not a perfect copy. I tried with the original Traynor iron 5.2k output and pt but voltages on the pt were too high 425 on plates of outputs resulting in a stiff cold amp. I ran it on a variac ramped voltages down to 100 vac and voila nice warm distortion little bit of cream. Much better. Did the math and for some reason came up with 265-0-265 power transformer. Custom ordered and just wired it in.

Distortion is amazing although not near as loud so I measure voltages. Now I have 324 on the output tube plates and I'm sure the preamp tubes are low voltage too. I may have miscalculated math on this one. Good thing is I can use this pt for my Liverpool build when I decide to do one.

I have no clean on the amp. Not on a Les Paul studio or my 74 strat. Not unless I put guitar volume on 3 and high strings still have break up no matter how I pick. Is this the low voltage causing this issue? If so how do I calculate the right power transformer for this amp? 325-0-325 was way too high that's for sure and I certainly don't want to make the same mistake twice.

Ideas?

Thanks Peter.

[Firestorm]

First of all, that's a nice scientific approach to finding a sound. But second, when dial down the voltage with a variac, you also dial down the filament voltage on all your tubes so they will have different emission characteristics and this makes a difference.

Certainly lower voltages on output tubes makes it easier to overdrive them. Since you like experimentation, you might consider running the filaments on DC with a variable output control. You don't want to run run them below specs, but filament voltage has been touted as a "master volume" of sorts. I know for sure that rectifiers can be run well below their spec voltages. Preamps and output tubes, not so sure. You can certainly run them at 5.7 or 5.8.

[lpd]

Maybe I will put a filament transformer inside and then experiment with b+ voltages. You are right on the lower heaters I didn't factor that in until after the fact :/ looks like sagging heater voltage makes a difference. That would explain breakup at almost no volume ie: too low voltage. I guess I need a higher rated transformer 280-300 I suppose.

[lpd]

Unless someone can suggest a voltage on the pt to bring from 324 to 390. I currently has a 265 volt pt but am not sure on the math to calculate the right one.

[lpd]

Ok I wa measuring voltages wrong. Still low though. I have 120 on my mains almost always. My voltages are:

B1 342
B2 324
B3 257
B4 243
B5 231

Looks like 50 volts below on most with exception to B5 may have to tweak. 300-0-300?

[Firestorm]

Reverse biased high watt zener on the center tap will drop B+ without affecting other voltages.(Down the rail voltages will change of course).

[lpd]

Reverse biased high watt zener on the center tap will drop B+ without affecting other voltages.

My voltages are 50 volts to low why drop with a Zener? I'm trying to raise 50 volts and if I can with a new PT that would be great. My other PT is 325 do you mean Zener on the 325 pt?

[Firestorm]

Reverse biased high watt zener on the center tap will drop B+ without affecting other voltages.

My voltages are 50 volts to low why drop with a Zener? I'm trying to raise 50 volts and if I can with a new PT that would be great. My other PT is 325 do you mean Zener on the 325 pt?

Sorry. Not paying attention. Now you're too low.

[lpd]

No problem. I think I'm going to go to the 300 volt transformer and keep the 260 one for a Liverpool.

[Firestorm]

If there's a particular B+ you want to hit, a new PT can help, but they're wound for ratios of the source AC, so it might be hard to get one that gets you to a precise secondary. You can manipulate the secondary voltage with zeners.

But it's the relationship between input signal and B+ that determines if the output will be overdriven. So can always attenuate signal before the output tube grid.

This is the basis of power-scaling with drive compensation.

[lpd]

No problem. I think I'm going to go to the 300 volt transformer and keep the 260 one for a Liverpool.

[geetarpicker]

425v (if it is an Express) is really not all that high. Both of my original Express amps are somewhere around 415-418v or so B+, when the wall is at it's typical 123-124v around here. Same goes for my two clones using Pacifics. Maybe your current voltages are actually too low compromising your clean headroom, and the stiff sound you were also dealing with was not just a voltage thing but something else. Just a thought?

[JazzGuitarGimp]

In following the paper trail from the Express BOM, out to the Toneslut website, it looks like the transformer has an HT secondary of 300-0-300 at 300mA.

[lpd]

425v (if it is an Express) is really not all that high. Both of my original Express amps are somewhere around 415-418v or so B+, when the wall is at it's typical 123-124v around here. Same goes for my two clones using Pacifics. Maybe your current voltages are actually too low compromising your clean headroom, and the stiff sound you were also dealing with was not just a voltage thing but something else. Just a thought?

The problem was all of my voltages were over spec by 40 volts. I wired the amp up to a variac dropped the voltage to 110 and voila much better browned out and no fizz on the top end. I figured a 265 volt transformer but now have no clean :/ I must have miscalculated. I'm thinking anywhere between 280-300 should suffice then I can fine tune. It had really nice cleans with the 325 volt transformer but was very stiff and felt cold. I'm gonna try a lower voltage pt and keep my 265 for a Liverpool build with my a-3800 transformer.

I hooked her up to a variac and ramped the voltage up 10vac and I had much better cleans so now to the drawing table.

[bcmatt]

I wish you had lent me that amp to use in Japan (100V wall voltage). Had to use a Jazz Chorus for tonight's gig.... And that was unfortunately one of the nicer sounding amps I got to use on this tour... Not sure what happened to this advanced technological society, but it is sad... They lost tubes and tone. The people are so kind, but they have it very difficult in the amp department. I feel so sad for them. Next time I will install a pt and bring an amp.