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  1. JJman

    Master volume in JTM45.... Can it be defeated at will via push pull pot?

    Hey, this Fonzarelli MV loads the PI outputs down as you turn the MV down. I don't think the Fonz would find this to be cool.
  2. JJman

    Power output question...

    1/2 of the human-perceived volume of 150 watts is 15 watts. That's why volume knobs are log taper.
  3. JJman

    SF Champ upgrade project: Questions, thoughts..?

    My 74 (Vibro) Champ was idling at 20watts on the 6v6 when I got it. Use an excellent 6v6 after changing the cathode cap. I guess a 6L6 would not need to be as excellent to take the voltage and/or current these amps run the output at.
  4. JJman

    Does biasing hotter give you more rms wattage?

    In the OP's example, hotter bias (compared to anything close to "normal") will result in less output power. This is from the "earlier" clipping which is often a goal. The reduction in power is minimal especially in the audible world.
  5. JJman

    For cathode biased amp, which way is more accurate to measure plate current?

    OT shunt method is not accurate depending on the internal resistance your meter adds in ma mode. This can be significant in this application, even in an excellent meter.
  6. JJman

    H303a Harmony

    Old wax caps like that are often leaking DC. Interesting how they added a power tranny but kept the higher filament-voltage tubes by ground-tapping the secondary. Much safer yet still lower cost with only one secondary.
  7. JJman

    Moding silvertone amp, locating cathode

    Keep in mind that the bright-cap/switch on a volume pot does nothing when the pot is cranked. And very little when almost cranked.
  8. JJman

    Retensioning tube sockets, when is it necessary?

    You could try testing with some "socket savers" for continuity. However, if the male pins on the SS are larger than "normal" it won't be a valid test and could make the sockets even looser. Or just leave them in and you shall be saved! Gently tilting the tubes around a little, with the amp...
  9. JJman

    anyone know if this tube tester will do a good job testing tubes?

    Very similar to my 920 model. I see an issue. I don't see a 9pin socket (e.g. for 12ax7 type tubes or el84 or many others.) My 9pin socket was changed when I got it and I changed it again myself due to poor contacts. Mine is from 1947 IIRC. It did not have EL84 or 6V6 on its roller but I...
  10. JJman

    Help!!! My new Bassbreaker 15 (with the fix) is unplayable...

    I jammed with a guy who brought his brand new Bassbreaker. Mediocre tone to me but maybe they sound great.
  11. JJman

    Problem with tremolo..

    As mentioned, we don't know if you changed only the PI or also the trem to the EC scheme. The 5E9-A trem modulates the cathode of the PI so changing (only) the PI to cathodine is likely not kosher. You would now be modulating the thing that modulates only one of the output tubes.
  12. JJman

    Looking Into Local Stash Of Nos/anos Vintage El34's - Help With Matching Pairs

    Set the bias to something a little cold on an existing pair you already have. Change one tube on one side and measure the milli-voltage on that side via the probe port. Assign that number to that tube and take it out. Put in another and measure and assign that # to that tube. Keep changing...
  13. JJman

    Open secondary on reverb transformer

    I would be concerned with WHY the secondary opened. The standard suspect would be that it was driving a shorted load.
  14. JJman

    More fun with Deluxe Reverb project (PT replacement, plus blackface)

    My '71 distorted above 3 until I changed out the original speaker. Have you tried a different speaker/cab?
  15. JJman

    2204 with PPIMV to make it more basement friendly?

    The problem you are referring to is with the taper of the pot. Get a new pot with a more logarithmic taper. Maybe the stock ones are linear? Larmar is cool and I like mine on homebrews and my '71SFDR but that's really a separate topic from correcting a taper issue.
  16. JJman

    Replacing a 4 ohm speaker with an 8 ohm

    The amp and the parents will be happier at 8ohms.
  17. JJman

    Effects Loop: Series or Parallel?

    Considering that plugging into a single jack can also switch other things, I don't know if one can universally predict the results of doing so on one end of a loop. Most newer bass distortion effects now use a "blend" approach which is sonically analogous to a parallel loop. If you have...
  18. JJman

    Advantage or disadvantage to have first filter before or after the standby switch

    Never noticed that change. The 77-78 would cause a much larger sudden draw from the rectifier when switching into "play" mode from an initial power up. Probably not a problem for a 5u4gb but I like the earlier approach. I think some amps have the standby between those 2 caps, so to speak.
  19. JJman

    Fender 6G16 Brownface Vibroverb - reverb mods

    I would try a cap across the 470k that goes to the wiper of the reverb control. Maybe 1000pf to start for experimenting.
  20. JJman

    Old Traynor Low Output and Red Plating

    Ultrasonic parasitic oscillation? I would add small caps to ground on each el34 grid as a test. ~2000pf or so.
  21. JJman

    Fixed Bias 2-EL84 amp suggestions needed for tube matching

    Epiphone valve jr. It is SE and less than $100 used. Just use a good voltmeter and measure the cathode dc once warm for a while. Tubes with the same cathode dc in there should be dc matched in a PP amp. If you use a PP amp for matching, you have to leave one tube in side A, changing out the...
  22. JJman

    Considering replacing all Capacitors in 65 Deluxe

    I removed all the Brown couplers in my '71 since the internet said I should. I kept them and years later tested them. They are all in spec and do not leak dc. I'll test them for ESR when I get such a meter one day. I'll put them back in when the internet tells me they are cool since they...
  23. JJman

    JMP 2204 Doesn't Clean Up

    Loosing highs while rolling the volume down is a common thing and depends on the pickups, pots, bypass caps (all in the guitar) and the load the amp's input places on the guitar. Amp wattage and amps tone controls and headroom and 98% of the circuit are not related to the specific phenomenon...
  24. JJman

    Spare rectifier socket pin for neutral AC tie?

    I was surprised the 1st time I saw an unused pin used like that. I choose to use wire nuts in my amps instead. I use a tie strap to ensure against strain and movement. Never has one come loose.
  25. JJman

    Best way to remove old Tolex glue?

    Could there be a Duct Tape solution here?
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