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In Reply to: RE: Bandmaster OPT posted by FenderLover on November 29, 2016 at 10:52:33
I was using a shorted rca plug to test:(. Just one of those odd issues.
Follow Ups:
So the amp "thumps" when the RCA shorting jack is in? But, doesn't if you remove this plug?The Vibrato/Tremolo in the Bandmaster, the anode voltage seems to come from point "B." The only filtering prior to this point is the choke (which is prolly ok) and the first filter stage (series 70mfd caps).
Did you change the leveling 220k-ohm resistors, in this first stage? May have some imbalance between those two caps. Not enough filtering for the VIBRATO portion?
I like using 220k-ohm 2-watt metal oxide or 5-watt wire-wound Mills.
Edits: 11/29/16 12/01/16
Thank you for the reply and ideas. I appreciate it and they are a great help.
I'll have to open the amp again and see if I changed out the 220k's. It's been years. If not I'll try that. I'll also see what's installed cap wise. I believe stock that the Bandmaster TFL5005D had a 5uf. I may have went to 10uf but probably not 25uf.
K40Y-9 take 50 hours to sound good and 200 hours to fully break in.
220K on the power tube grids does not change the sonic signature. It keeps the power tubes from running away.
I'd had some 5mfd/50VDC caps a long, long time ago. Used 10mfd/50VDC and even 25mfd/50VDC. No difference in the tremolo tone, that I can tell.
An 8mfd/150VDC Sprague ATOM will fit, in that position. AES now stocks 5mfd/50VDC ATOMs.
I wonder if I have the wrong tube in the spot. I'll have to check on it.
I am not sure I would go with 6U8 or 12DW7 phase splitters. Any 12AU7 as in 1/2 of the 12DW7 are not good sounding tubes. I know a phase splitter is not as critical as preamp circuits, but every tube counts. 6U8s are ok, but still not an audio tube.
The best 12DW7 by a long shot were CBS 12DW7s. They are very rare now. It may take over a year just for one to show up on ebay.
I do not see your link for Fisher mods, but I will share exactly what I performed.First I built a new RIAA with discrete components plus the fix for better low end. Frankly, I heard no difference from the stock RIAA.
I replaced all coupling capacitors with K40Y-9 including the phono section. I lowered the 7868 or 7591 with 220K grid resistors and changed the .047uF to .068uF at the power tube grid.
The power supply doubler changed to 2x 680uF 400 volt capacitors. Added a poly type 10uF capacitor on the doubler output. Change rectifiers to UF4007. Kept screen at 40uF, all others at 50uF.
Added two 3500uF for the bias supply & changed bias bridge rectifier to UF4007;
Used short plate Westinghouse 12AX7 or Brimar CV4004 in phono section. These tubes greatly clean up the phono section. Preamp section used RCA 12AX7 tall plate. Either black or grey are good with no noise issues like some black plates. Used vintage Tung Sol 12AX7s at phase inverters. RCA or Sylvania 7858 or 7591 finishes the tubes. Should mention a 12AT7 was used in the multiplexer output regardless if marked 12AX7.
After these mods, the clarity was greatly improved. The phono section was stunning- such a difference. It had a little chime in the audio that made it so musical sounding. Chime being like a church bell ringing if that makes sense.
Edits: 11/29/16
Sony, thank you. I have to open mine again to see what I used for the doubler etc. I know that I increased it but I can't remember to how much. I forsure did not add the poly cap.
Here's a link to my post with the links to Dave Gilespie tweaks.
http://audioasylum.com/forums/vintage/messages/23/237783.html
Believe it or not I actually liked Cornell Dubilier DMT caps in the output stage more so than the russian PIO's. They are polyester film/foil. It could have been that I didn't give the k40's enough time to run in etc but I've liked them in other rebuilds. I had the DMT's installed first so I may also have grew use to their sound.
http://www.mouser.com/ds/2/88/DMT-12545.pdf
http://www.mouser.com/ds/2/88/DMT-12545.pdf
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