AB165 Bassman mod advice (any techs in Saskatchewan?)

[brickthicket]

For the most part, I think I know what I want done. This is mostly going by clips/videos I've heard.

1) 3 prong cord (Got some nasty shocks with the 2 prong).

2) Stock AB165 normal channel pre-amp (any mods to get the best cleans on this channel?).

3) Tweed/Marshall mod on the bass channel (using deep switch to change from tweed to JTM45 tone)

4) Mid control pot for Bass channel (in place of ground switch)

5) Cathode biased - is this crazy? I want a warmer, quieter amp with more sag, and this seems to be the best way to achieve that. Plus I like being able to change power tubes without biasing.

6) Not sure about negative feedback loop. I've read about people changing/removing this section, but I'm still not sure what I'd prefer. For the most part, I want a warm, organic sound for clean and light overdrive (mainly for blues)

The main problem is, I don't know any techs where I live (Regina, SK). I know people who can follow a circuit, but they don't have experience working on amps, ie. they can't give me advice on the feedback look etc. Anyone around here from Regina or neighbouring area? I'd prefer to not ship the amp across the border.

Thanks!

[Stevem]

I just finshed changing the bias a bit on my buddys Highwatt 50 to let him run JJ electronics 6V6s.
This let him drop the amps wattage down from 60 RMS to 29 or 19 watts RMS dependant on the setting of his impeadance switch.
Now he can use the amp with its 4 -12" cab in smaller clubs with out going into a poor sounding attenuator.
You do not want to mount a mid pot way down near the old grounding switch hole as the amp will surly oscilate on you!
On my 67 bandmaster I added a mid pot to both channels, but my amp had been beat up by its former owner and already had holes in the back in the preamp tube area.
So unless you are willing to have holes drilled in a nice vintage chassis, your best bet is to find someone to work with and find what value slope resistor( the resistor that takes the place of a mid pot) provides you with the best average a level of mids you want, or get graphic type EQ pedal to place in front of your amp.
Cathode bising the output stage is a great way to get more bluesy sustane from the amp, and a switch for that could be stuffed into the hole that held the ground switch.
By far the biggest changes tone wise will take place in the preamp section.
The first preamps tubes (V1, or V2 dependant on the cheannel) set the whole tonal stucture for the rest of the amp.
Just swapping different brand and type tubes can greatly effect the amps overall tone nature.
Of course you could learn to work on amps yourself, hey its winter, got any better things to do? LOL.
These fender amps are the easyest ones to work on and mod due to there build and layout.
If you get the Torres engineering book"Inside tube amps" I would bet you could by late spring takle these mods your self!
Its a simple read, but tons of great info in a large printing format.
Good luck!

[Jana]

1. good idea

2. it's setup for cleans already

3. it's going to take more than a switch to change from tweed to jtm45

4. use the deep switch to switch different resistor values to select different mid settings (the slope resistor is not the resistor you want to change).

5. not advisable. The transformers you have will not be up to the task. Cathode biasing will give you less sag anyway.

6. The feedback loop could changed to feed the inverting input of the PI like most amps.

[pops]

If you have access to tubes, i would change all the 12AX7's to 12AY7's, you can take the bypass cap off the preamp tubes, use a switch if you like to go back and forth or just unsolder one at a time an see if you like the change. You could also run 6V6's and bias for those for a much warmer sound. They are close enough the the 6L's that the transformer won't mind. If you like it go with it. You can also do these one at a time and see what you like. It won't be a JTM45, but you might like it without really modding the amp.

[ToneMerc]

If it was me; I would remove the existing main board and install a 6G6B board. Set the bass channel slope resistor and tone stack like a JTM45 and setup the normal channel like the Blonde or BF amps. Then use an A/B box to switch between two totally different front ends.

TM