Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: who...me? on May 19, 2017, 07:25:38 am
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Last year I built a Princeton Reverb kit (AA1164) that I purchased from Mojotone. The build went smoothly, and I've really enjoyed the amp. After awhile I realized that my amp didn't have the same breakup characteristics that you'd normally associate with a Princeton Reverb. After digging around a little I noted that the Mojotone schematic has more voltage going to the phase inverter (aka Stokes mod). I replaced a couple of resistors, moved some wires and returned everything to original spec. However, while I am getting some breakup, it's not a early on the volume knob as I'd like. I've seen videos with nice crunchy distortion at 5 and I'm on 7-8 and still not as crunchy as I'd like. I'm trying to determine what options I have to produce the tone I'm after, or if the components of these older amps have just drifted far enough out of spec to produce these tones. Any insight is appreciated.
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Could be a lot of things. The drift that you spoke of, speaker, tubes, output transformer, neg feedback.
Try a few things to see if you can get the tone ur looking for. If you have a different less efficient speaker, try it. Lift the neg feedback resistor and see what it sounds like or try a smaller value. JJ preamp tubes seem to be good and strong as are the power tubes, but the power tubes are a little different type 6V6. Might try some EH or Tung Sol power tube which are a little more like the old RCA type.
Don't get hung up on pot setting, they will be slightly different from amp to amp.
BL
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... I've seen videos with nice crunchy distortion at 5 and I'm on 7-8 and still not as crunchy as I'd like. ...
I used to own a '67 Princeton Reverb (actually owned quite a few silver- and blackface Princetons & Princeton Reverbs). It got a little "furry" by 4 or 5, distorted some by 7, but never got "crunchy". Diming the volume gave a fairly unpleasant distortion.
You might be hearing the amp as it actually is. If I really wanted that amp to be crunchy, I'd just use a pedal. In fact, I often did use an old Fulltone '69 with the controls pretty carefully set for a full, tube-like distortion at any volume.
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It's so hard to describe tone. Here's a video of one that sounds really good and has nice breakup. https://www.youtube.com/watch?v=POHUM632k88 (https://www.youtube.com/watch?v=POHUM632k88)
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A 12" Greenback will crunch it some. The example you posted is a 10" Fender Ceramic. Speakers in Princetons are a very big deal. I have one with a 12 inch JBL that will not breakup and another with 2, 10" CTS AlNiCo that breaks up nicely.
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Ditto to Hotblue.
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I just went the other way, which is to provide more clean headroom to a DRRI.
Tubes and speakers were significant mods for our purpose.
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I've been rolling different tubes through it. So far the TAD 6v6gt-str have sounded the best to me, even over a set of RCA's. When I built it, I tried several speakers and landed on a 10" Warehouse Veteran - 20. Any speaker suggestions are welcome.
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The link is a folder containing 3 clips of my unmodded 1967 Princeton Reverb at volumes 5, 7, and 10
Electro Harmonix 6V6EH output tubes. Probably 15 years old, but with not many hours use.
Weber VST P10R Alnico classic speaker (from before the Jensen lawsuit that made Weber change their model names)
1975 LP Standard with Bill Lawrence humbuckers with push-pull coil split switch on tone control.
First part of each clip is bridge pickup single coil, second part is bridge pickup humbucking.
Bass & treble on 5, reverb and tremolo off.
https://drive.google.com/open?id=0B2SlnKIIH7A3dXBobENseXY1VTA (https://drive.google.com/open?id=0B2SlnKIIH7A3dXBobENseXY1VTA)