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Tweed Deluxe: Managing the Heat

Discussion in 'Amp Tech Center' started by gabasa, Feb 28, 2021.

  1. dankilling

    dankilling Tele-Afflicted Silver Supporter

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    Comfortably warm is pretty normal for this style amp. I’d play it a while and only change out the choke if you want to see what it changes in terms of tone and feel. Enjoy!
     
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  2. gabasa

    gabasa Tele-Meister

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    Thanks so much @dankilling, as well as everyone else who's helped here.
    I'll post some updates in a while.

    For now, I've actually taken all the measurements in the cream 5E3 I recently built and punched the numbers into robrob's tube bias calculator. That amp ended up at exactly 100% dissipation, so screw it, I'm warming up the iron again and will up the value of the cathode resistor to 300r in that one, too.

    This has been really helpful for me.
     
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  3. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I would play it for a while and hear if you like it. Removing the choke will reduce the voltage on the screens but... sometimes that *improper* voltage on the screens gives an amp a certain something. Champs are known for it. lol.

    Now that the heat is reduced a little, do some critical listening. I would leave the other amp at 100%PD if it is not having the heat issue. OMMV.
     
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  4. gabasa

    gabasa Tele-Meister

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    Funny you mention that, the reason I started using chokes in my amps is because I was amazed at what one did to my Champ.
    Thanks again.
     
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  5. The Ballzz

    The Ballzz Tele-Afflicted

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    @gabasa

    I'm confused about your dropping string choice. I understand the choke, but am curious why you chose a 22K downstream, while the Fender schematic shows 10K? Are you endeavoring to compensate for lower current draw of the 6AT6, that I'm not experienced with? Or were you trying to make up for not having a dropping resistor for B2? Am I missing something, or did you go from someone else's schematic?
    Just Curious & Trying To Learn,
    Gene

    Deluxe-5D3-schematic.jpg
     
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  6. gabasa

    gabasa Tele-Meister

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    Hi Gene,

    I was thinking about the exact considerations you mentioned above. I didn't know which value to use for that particular resistor, but because this is a 6AT6 amp and has one triode less than the 5D3, I thought to start with the dropping resistor value used in the Harvard, which is 22k.

    Even with the 22k, the preamp voltages are kind of on the higher side, so I stuck with it (and I'm really digging the sound!)
     
  7. Nickfl

    Nickfl Friend of Leo's

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    I wouldn't, I would see how you like it with just the cathode resistor change and then try screen resistors while keeping the choke. I also wouldn't put a resistor in series with the choke, do one or the other, but I think you should be able to get it where you want it with the choke.
     
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  8. gabasa

    gabasa Tele-Meister

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    I'm really liking the sound of this one, it's addictive.

    Update: After exactly an hour of playing tonight, the top of the chassis wasn't quite as hot as last night, but the PT ... I couldn't touch it for more than a few seconds because of how hot it got. Every voltage in the amp checks out, so I think that it's just the design of this PT that it heats up quite a bit. Fwiw, it has a great track record in Victoria's 20112 and Ivy League amps.

    In comparison, I swear that the Hammond 290BX I have in my older 5E3 runs a lot cooler. I'm going to test it out and get back.
     
    Last edited: Mar 2, 2021
  9. gabasa

    gabasa Tele-Meister

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    I just did the same modification to the beautiful cream 1x10 5E3 I also built recently. It's got a 10" speaker but that amp sounds so good.

    Doing the calculations on robrob's website, the power tubes were at exactly 100% dissipation. After modding to 300r cathode resistor, it went down to 93.7%. It just feels better this way. I never really crank my amps, even with the band, so maybe it's tougher to hear the tonal differences at lower volumes.

    Next up: I might order some 1k/5W Mills wirewound resistors and replace the 470r screen resistors with them. I've read a lot about keeping the screen voltages lower than the plates (mine are higher). Let's see if this does the trick ... I've read that this can reduce both plate and screen currents.
     
  10. lathoto

    lathoto Tele-Meister

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    I had a Deluxe that ran hot. I put JJ tubes and an EVM12L in it and it sounded better and ran a little cooler (but not much).
     
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  11. JamesAM

    JamesAM Tele-Meister

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    Hi there- I went through a heat/bias exercise here last summer with the kind folks on this board and got down to high 90s% dissipation on my 5e3. I had to use a 330r cathode resistor, and it still runs kind of hot after about 45 minutes- ironically with a 290BX, the PT that you mention runs cool on yours. I can keep my hand on it for maybe 5 seconds before it becomes too much? Voltages are all reasonable and the amp sounds great with no issues since I rebuilt it last June.

    I was really concerned until I bought a brand new PRRI, and that sucker gets waaaaay hot compared even to the 5e3- the heat even transfers through the chassis to the faceplate after about an hour. I’m not sure if it’s the small cabinet, the inefficient configuration of the tubes, the individual variance of PTs, or a combination of all of the above, but it seems to be fine for both amps. I’ll be sure to post if anything happens with either amp, but so far so good.
     
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  12. gabasa

    gabasa Tele-Meister

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    Thanks for all the info, it's helpful. Here's a question about the screen resistor suggestions.

    If I remove the 470 Ohm screen resistors from this amp, and replace them with 1k:
    • How much of an effect could this have on my screen voltages?
    • How much would this affect my plate voltages?
     
  13. dankilling

    dankilling Tele-Afflicted Silver Supporter

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    Voltages won't be dramatically affected by this, but you might lose a little 'top end' from the amp. It might not even be noticeable.

    Bigger change here will be the bias. Recheck the bias if you put the 1k's in place to be sure. Bias changes will affect tone more than the screen values at 1k, IME.

    And as always, one change at a time until it's right. Too many changes at once can throw things sideways fast.
     
  14. gabasa

    gabasa Tele-Meister

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    I’m actually thinking of trying out a 330r resistor tonight, just to see how that affects things.
     
  15. Guitar-Rocker

    Guitar-Rocker TDPRI Member

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    I'd try a 330R or a 360R, common sizes to obtain. Replacing the 470R with a 1K will probably be of no effect.
     
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  16. The Ballzz

    The Ballzz Tele-Afflicted

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    Here's what I might likely try for your 5D3. Given that there was no choke involved in the original design, you may want to play around with it's position. For example, put it before the OT/CT node and the try a 5KΩ just prior to the screen node and then play around with the value of the resistor that is currently 22KΩ, to keep your PI and preamp voltages where they are, or even a tad lower, as you claim they may currently be a tiny bit high.
    Just A Thought?
    Gene
     
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  17. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    How about coming at this from a different direction. Dropping the B+ can also help to cool things down. A Bucking transformer is one option.

    Check out this thread questioning a drop in B+:
    Backup Diodes?
    Discussion in 'Shock Brother's DIY Amps' started by The Ballzz, Sunday at 1:44 PM.

    I don't think you have backup diodes on this amp. This mod would be kind to the rectifier tube and may drop the B+ to help reduce the current demand resulting in a cooler PT.

    Might be a win win.
     
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