Search results

  1. D

    Upping 5F1 6V6 Plate Dissipation… raise Voltage or lower Resistance?

    It's actually the opposite KF...dropping the cathode resistor value will cause the plate voltage to drop as the power tube begins to draw more current from the power supply. The increased demand on the power supply will cause voltages throughout the entire amp to drop.
  2. D

    Pulling out my speakers on my Tone Master Twin Reverb.

    Speakers will occasionally stick to the baffle board because they were installed at the factory while the paint was still wet. If yours seem to be stuck, gently work a thin putty knife all the way around to loosen the bond. Just don't push the knife in more than a 1/2" or so as you risk damaging...
  3. D

    Bassman sounding off. Help

    NTC makes a great point! It's very easy to measure right there on the pilot light. Just make sure your hand does not brush across any other part of the circuit while taking the reading. Set your meter to "AC voltage", place red lead on one of the wire lugs and the black lead on the other.
  4. D

    Ultra Clean Push-Pull EL84 design?

    I will agree that you can get a bit more out of the EL84's with a bump in plate voltage and a larger OT. I built a Friedman JJ Jr clone last year with a large 40 watt/8k OT and a B+ of 380vdc. Even with the EL84's, this amp has plenty of headroom and grunt and it gives some of my larger builds a...
  5. D

    [newb] learn from my Variac mistake.

    A 60 watt bulb will work just fine on a smaller amp and it limits the current enough that you won't risk damage to the expensive transformers or other components.
  6. D

    Bassman sounding off. Help

    If you can safely measure your filament voltage try both voltages and see which gets you closer. You are shooting for 6.3vac but you should be safe 10% in either direction.
  7. D

    Ultra Clean Push-Pull EL84 design?

    EL84's are so easy to drive in to distortion that you rarely see "high headroom" and "a pair of EL84's" in the same sentence. If you had more space in the chassis you could add two more but it seems you are quite limited on space.
  8. D

    Liverpool 15w?

    I was just thinking about a similar build earlier today. I have a box full of nice old stock EL84's that I need to use up in something.
  9. D

    [newb] learn from my Variac mistake.

    Go to the local auto store or hardware store and pick up a 60-100 watt "rough service" bulb for the older style drop lights. They usually have a thin rubber coating over them to prevent accidental breakage but they are incandescent and work perfectly in a limiter.
  10. D

    Bassman sounding off. Help

    Did you bias the amp with the wall voltage at 220 and now it has jumped to 243? If so, you should definitely rebias for the higher voltage or find a way to run the amp at a steady 220. Another thing to consider also is that the tube's filament voltage will be excessively high if your PT is...
  11. D

    Grounding multiple shielded signal wires

    I think it will be fine. I have grounded the shield to a circuit ground buss or a close spot on the chassis and have never had any problems with added noise. Grouping the shields together should not be any different than landing them all separately to the same grounding point.
  12. D

    Coupling Caps-Fender Amps-Voltages

    Yep. 400v caps seemed to be the norm for many years. Now that technology has allowed manufacturers to make higher rated caps in a smaller package, many caps are now rated at 630v. 400v will work fine in many circuits but some amplifiers have a B+ voltage of 450v or higher. In these cases a 630v...
  13. D

    It's oh so quiet

    This same issue will pop up in new builds occasionally. In some cases it will be the PI cathode resistor that sits between the two 1 meg resistors on the board. Your schematic calls for an 820 ohm so double check that you didn't accidentally install an 820k by accident. This biases the PI very...
  14. D

    Trying something different…just like before

    Can't wait to see the completed build.
  15. D

    plate driven TMB

    Did you mean to write 5F6-A? The 5F2-A is a Tweed Princeton circuit.
  16. D

    RobRob Deluxe Micro Build - Measured Voltages - Advice Needed

    Double check your resistor values in that area to be certain you didn't make a mistake. I like to measure each resistor before installing to eliminate issues like this. You can try measuring them in circuit but some of them will not read accurately because they are in parallel to others on the...
  17. D

    Presence control

    Adding a cap across the feedback resistor will only dull the highs. It allows the higher nfb frequencies to go around the resistor and act on the power amp by dulling the high end. Introducing nfb is suppose to extend the frequency response but I do agree that in some circuits, I have also...
  18. D

    Presence control

    Many amps use nfb without the added presence control while many of the larger amps with more features have a presence control. Are you simply looking for a way to increase the higher frequency content or a way to remove some of the higher frequencies? A "cut control" mod is a simple way of...
  19. D

    Presence control

    The presence control is simply a filter on the nfb circuit that will make your amp slightly brighter in the really high frequencies or slightly duller. You can have nfb without a presence pot but you can't have presence without an nfb circuit. A resonance control is very similar but it works...
  20. D

    5f6a DIY build develops squeal

    It's not unheard of for the OT wires to be wrong and the amp will never squeal. It is strange that putting a lower gain tube in the circuit caused the amp to start squealing though. Did you make any other changes while swapping the tube such as moving any of the wires? Was the amp inside of it's...
  21. D

    Mostly finished first build - but . . . (speaker help needed)

    I believe that Tone Tubby makes a shallow speaker for tight cabs. I remember it seeing while browsing their sight.
  22. D

    Oscillation with high NFB on 5F6a

    I would try it without shielded wire first. Just make sure the wire runs straight to the pot as much as possible and don't let it run parallel to the tonestack wiring.
  23. D

    Oscillation with high NFB on 5F6a

    I know from building several of the Marshall circuits that the routing of the nfb wire from the board to the presence pot can cause instability if routed to close to the tonestack wiring. You may be able to adjust that wire a bit and get rid of the cap.
  24. D

    Radial vs axial capacitors

    If you are wanting a name brand cap such as a Sprague, the cost can be quite high. There are still much cheaper options for axial caps available though if brand does not matter. "JustRadios" in Canada has 450v axials for $2-3 dollars each and "Antique Electronic Supply" has several options for...
  25. D

    '55 5E3 hums louder as it warms up.

    How old are the other electrolytics on the board. The smaller 25uf caps may be dried up if they are originals. Preamp tubes can also be a source of hum from either heater to cathode leakage or becoming gassy.




Top