New 5E7 Bandmaster build bug

[POWDOG]

Hi all. Just finished a 5E7 Bandmaster build. Sounds great until I turn up the volume and hit a hard chord. It makes a "chirping", garbly sound which diminishes as the chord does. Sounds like a cold solder issue, but I can't replicate it by banging on the amp. 435vdc on the plates, biased at 40mA. Tried different tubes, no change. Ideas? Thanks!

[xtian]

Could also be blocking distortion, which means you may have to limit signal along the chain.

[POWDOG]

Hi guys. Got the big out of the amp, but concerned about the high voltage. Using a Heyboer HY022798 PT from Weber, which is their Bandmaster application, it has a 370-0-370 secondary which using a 5U4 is producing 470vdc at the first filter cap, 375vdc at the preamp plate resistors and 455vdc at the 6L6 plates. Also;
V1 Pin 1 201vdc
Pin 6 202vdc
V2. Pin 1 205vdc
Pin 6 320vdc
V3. Pin 1 250vdc
Pin 6 308vdc

Do these seen scary high? I could use a 50v Zener on the B+ center tap or just swap out a Hammond P-T290DX for the Heyboer. Thoughts? Thanks.

[Tone Lover]

So what was the bug share with us.
Bill

[POWDOG]

Well, I used a layout that I printed off of the Ceriatone website (nice and colorful, you know). Unfortunately their layout clearly shows the leads from the PI running to pin 5 on the 6L6's, and the 1K5 resistor going to pin 6, which is of course backwards. Reversed the leads and that was that.

[Stevem]

All your preamp tubes voltages seem fine, if you want a bit more preamp tube dirt sooner with a tad less tp end responce, than add 5 to 7k more resistance to the second power supply dropping resistor and make sure its at least a 1/2 watter.
If I recall right this resistor in a stock 5E7 is 10k.

[pops]

If you are concerned about the high voltages a choke in front of the first filter cap will lower your voltages better than the zener trick. It has to be big enough to handle the current of the power tubes as normally a choke comes after the power tubes. I have done this and it works very nicely.

[POWDOG]

Actually, being a new build, I ramped the amp up on a Variac to 120 vac to form the electrolytics. I then foolishly checked the voltages with the amp still plugged into the Variac (still set at 120 vac). When I finally decided to check the amp plugged directly into the wall outlet, all voltages dropped about 30 volts across the amp, bringing me within about 10 volts of the original 5E7 values. Pretty dumb mistake! Oh well, live and learn.

[Tone Lover]

So how are you liking the amp, I have a 5E7 chassis sitting here I meant to build a long time ago. I never got around to it.
I seem to have a split personality (LOL). (Blues amp) (High gain beast) I cant seem to make up my mind so I have several of each sitting in my jam room.
Bill

[POWDOG]

Well Bill, I've always been a "5E3 everything on 11" kinda guy. I really didn't build the 5E7 properly, as I used a multi-tap OT pushing a pair of 10" Weber alnicos, not the 2 ohm OT into three 10" speakers. So I really haven't honestly experienced the amp. As is, I was under impressed with the amount of gain, so with some bypass cap and treble cap tweaking I made it into a "jazz" guitar amp, which it does well. The next 5E7 I build will definitely be a 3 x10" amp, using the proper OT and probably feature some gain mods. Still, I gotta say that even as built, with the volume dimed, a pretty cool sounding amp.

-Ethan

[Structo]

Another thing that can cure blocking distortion is upping the value of the swamp (grid resistors) resistors on the power tubes.