Slowly getting my bandmaster back together

[Quencho092]

I found that the 470 ohm screen resistors over the power tube sockets were way out of spec. One of the power tubes was not lighting up or getting warm at all, its probably toast.

My amp is a AA763 revision. It doesnt have the 1.5k stopper resistor? (is that what its called?) over the power tube sockets like the AB763 has. Does this benefit the circuit/enhance the sound/reliability of the amp? I'm guessing that if it was a part of the revision, it's worth implementing to protect my amp and the tubes.

I replaced the filter capacitors with F and T german capacitors. The amp fires up perfectly fine, except for high distortion and 1 power tube being dead basically. Hopefully after i replace those resistors and put a nice set of power tube sockets in there (I was going to retension but these sockets are all bent out of whack and tarnished to hell) it will be up and running again.

I had 7581A philips tubes, but they're probably dead by now after those screen resistors dying.

What's a good modern clean sounding tube that will work well in my amp after it's all fixed up? It's a blackface amp, i like the sound of it, especially the cleans. I plan on using my 15 inch alu dome weber JBL copy, and i play funk/jazz/fusion, so headroom is key. I don't want NOS, im tired of the hassle and EXPENSE. 6L6? KT66?

 

[jeremy]

Re: Slowly getting my bandmaster back together

tad makes two great 6L6 versions, i prefer the middier short bottle (ge style) but the tall bottle (rca style) is a little cleaner and more balanced to my ears

 

[Stratman]

Re: Slowly getting my bandmaster back together

Your transformer can not handle KT-66 because of the current draw for the heater circuit.

1.3A = KT-66 * 2
0.9A = 6L6 * 2

 

[Quencho092]

Re: Slowly getting my bandmaster back together

gotcha stratman!

You know i noticed something. My DRRI gets smoking hot when its on for a while, but my bandmaster's power transformer is always cold like as if it's powering the amp without a problem.

Gotta love it when things work like they should.

Never tried a TAD. The tubes i have tried are sovtek 5881's in my peavey classic, and winged C 6l6's (SED?). Currently i have 7581A's in there, but im gonna take them out because i think they might have gotten killed by the bad resistors.

I'll take your word for it jeremy and give those TAD's a go. I've heard alot of good things about them, but i've been out of the gear loop for a bit so i've forgotten the 'street knowledge' that my experiences and this forum have helped me acquire.

They're nice and clean right? I'm very big on cleans, since a non muddy tone at decent volumes is critical to the music that i play.

 

[ES350]

Re: Slowly getting my bandmaster back together

Get the 7581's tested; they may be OK. The next best thing to the 7581A's are the Sylvania STR line, which are not very pricey for NOS. ANOS 7581's are a bargain and my last two sets were 80$ total. Biased properly, the Winged C 6l6GC are probably the next best thing for clean 6L6 power...I think you'll find that you need that 1.5 K resistor. I have had a few problems with late 60's Fender power tube sockets; I have been replacing them since it seems their time is up...

 

[Quencho092]

Re: Slowly getting my bandmaster back together

I replaced both power tube sockets, and put in that 1.5k resistor according the the BF AB763 schematic.

I'm pretty pumped! I've been checking the values of other resistors on the board and they're all within 5% of tolerance!

So Filter Cap replacement? CHECK. Power tube socket and resistor replacement? CHECK.

Just out of curiosity, what does that 1.5k resistor do exactly?

And if i try the amp out with the 7581's that may be toast, will the resistor blow?