Fender Bassman PI (1966 Sept) AB165

[groovyfingers]

Posted about this sometime ago. Finally said I must finish before moving on to Gibson amp. I had purchased parts, replaced filter caps, and let it sit for about two years. I have now replaced one power tube socket (arching between terminals two and three on original prompted replacement), the 470 ohm screen resistors, the 1500 ohm control grid resistors (btw, mine didn't have the 220k feedback resistors from the plates of the power tubes back to the grids of the power tubes installed like the AB165 schematic shows), the bias cap, the bias circuit back to a "bias" circuit instead of the hum circuit, changed the feedback circuit back to an AA864 circuit, removed the 500pf and .01 caps across the 100k plate load resistor, and will reverse the speaker side of the output transformer by connecting the green to positive and the black to ground. I've got to purchase some more parts, some for this amp and some for the '41 Gibson amp. I'm getting an 820 ohm and 100 ohm resistor for the feedback loop (had to think about this some) and was going to replace the .022/400 blocking caps between the plates of the phase inverter and the grids of the power tubes to .1 or .047. I'm going to put in a Pentode/Triode switch as well, got the parts for it. Please comment on any of this, if you would. Questions, I was going to use 400v orange drops for the .1 and .047 caps (also a .001 coupling cap), is that fine or should I use 600v? How would you describe the differences in sound/tone between the .022, .047, and .1? Also, I see in an AB864 schematic, a 500pf coupling cap to the phase inverter. I was going to go with a .001 here, what difference would you describe between the two? I have the 500pf I pulled and was considering trying it as well as the .001. As you all can tell, I'm not an expert by any stretch of the imagination. I thank you all for the knowledge you provide here, and elsewhere for guys like me that enjoy this.

[groovyfingers]

Search has answers

Used the search for "Orange Drop" and found some threads that were real helpful. Questions like mine have been asked before. I'm going to go with 600v polyester and polypropylene for the .047. I'm going to hear the differences between the stock .022, then the .047, and lastly the .1 and see what my ears like. I'll also try the 500pf, then the .001 coupling cap to the phase inverter and see what difference lies there.

[Five_E35]

Are you also converting the amp to the Andy Ruhl mod -

http://www.blueguitar.org/new/schem/...4_vs_aa165.pdf

If so I'd be interested in how it works out. There have been a few SF Bassman & Bandmaster heads recently on the local Craigslist at really good prices. Do people play guitar through the bass channel on these amps, or hot rod it for more gain?

I've been thinking a 1x15 Bandmaster combo with suitable OT and something like a JBL K130 would make a great amp for a baritone Tele, Fender IV tic-tac bass, or even steel guitar.

[groovyfingers]

I've been outed

Yea, this is what I used, in addition to these forums, Aspen Pittman's book, and the information available on Hoffman Amps and other web sites over the years. A big thanks to all. Of course, I'm waiting for a few more parts to complete this project and hear what I've done. I'm thinking of just disconnecting the ground switch and forgetting the pentode/triode switch mod. The 6L6's stock plate resistors are 470/1watt resistors, I changed them to 470/3watt metal film resistors and hung them off to the side of the tube socket. Can someone tell me why the mod uses 1K/5watt here? Would I get in trouble if I used a 1K/3watt? Thanks.