Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jy67 on February 21, 2022, 08:08:44 am
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Following the mods from this site (http://acruhl.freeshell.org/mga/main/AA864_vs_AB165.html), would this layout work in converting the AB165 phase inverter to AA864 specs?
https://photos.app.goo.gl/4FdFeqXegAemgwg99
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You need to swap positions with the 100Ω and 820Ω.
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You need to swap positions with the 100Ω and 820Ω.
Thanks!
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The 0.001pF has to be 0.001nF = 1000pF.
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Correct me if I'm wrong, but if I wire it like this (new version attached), I use the existing jumpers that are under the board(the black traces).
It seems like it might be the least invasive way to convert the circuit.
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You replaced the nice blue molded caps, another option is to use blue molded caps from the PI section in the first gain stage, then use the ones from the first gain stage in he PI section. This will keep all the blue molded caps in the circuit and give the Bass channel more gain. I made that change in my '67 Bassman, it sounds awesome!!
Just a thought!!
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Here is a pic of my ‘67 Bassman with AB165 to AA864 conversion. I removed 1 or 2 jumpers from the back of the board in the PI section. Also you can see the blue caps I swapped between the PI and 1st gain stage.
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I had one of these Fender 50 watt Basssman AB-165s for a long time. It was the first amp that I ever bought. I got it and the 2-15 cabinet back about 1979. I used it to play bass through with a local band for a long time. I sold it about 5-6 years ago, long after I was no longer playing in a band.
The only problems that I had with the amp, other than re-capping the power supply, was the leads of capacitors in the preamp breaking, probably from vibration while playing. The first one was hard to find, after that, I knew to look at the leads when I had an intermittent sound problem.
The one I had was built in Santa Anna, CA, according to the label inside the amp case.