Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Platefire on April 20, 2024, 11:43:13 am
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The issue is with the hot switch engaged. When I have the Pre-gain cranked up and the master volume to 100% for the highest measure of gain the sound goes into cutoff in the range of 80%to 100% vol. Was wondering what I need to do to correct this? Schematic is attached
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How about an 80k plate resistor on the "hot" stage?
On the other side, looks like you have 1M of ground reference for the grid through the volume pot. Maybe another resistor from grid to ground?
Dave
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sound goes into cutoff in the range of 80%to 100% vol
stays off, or builds back up?
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Stays off! No slight transition. Just cuts off like someone flipping a switch when the volume reaches that 80% position. When I say "cut off" I mean volume. You can still hear some low volume sound but it's not clear and is garbled.
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The 5D3 has a 1000pf cap between plates of the PI which isn't on your schematic. Maybe you're into oscillation at high volume?
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I'd "temp in" a 1M in place of vol pot, so 1meg pin 3 to ground, switch to "new" junction of pin 3 & 1M
if the pot is "opening" you lose ground Ref to pin 3 as the other dave pointed out.
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OK Thanks! Bare with me :think1: We are talking about the temporary 1Meg to ground onthe master volume input(3), right! Then switch to the hot switch position and try it live? I'm a little confused. How do I test it, with a multi-meter or just playing the amp live? Sorry!
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Are you sure it's wired like the schematic?
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Not checked lately! built it in 2007 and modded it to add the hot switch 2011. But you know me, I never make a mistake :l3:
Seriously, this is a build I did with spare parts I already had on hand. That's why some of the coupling cap values are kinda
higher than Fender values. It only started the cutoff issue when I added the hot switch
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It only started the cutoff issue when I added the hot switch
That's why I asked. :icon_biggrin:
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I'm sorry I got my issue description wrong. I just went and fired it up and refreshed myself on it.It's when the Pre-volume is 80% plus and the Master Volume is about 1(high gain, low volume) with the hot switch on.
I tried it about a month ago and it was cutting off at that setting so I sprayed a lot of Deoxit on
both volume pots and didn't make much difference at the time. So on the latest fire up the volume was holding up pretty normal at that setting, it's just some static in the signal now. So it
appears the Deoxit did some good in the long run. These pots may just need changing
Sorry, I should of fired it up and checked it again before I posted. Can I blame it on old age?? It was nice talking to you guys though!!Platefire
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Can I blame it on old age??
:laugh:
I went to put the toaster n butter away, since I was holding the toaster n seeing the butter tub, I attempted to put toaster in fridge. yep you got my permission
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For those of you who wasn't hanging out here when I did this conversion, you need to see this! You've seen the schematic but this is what the real amp looks like :help:
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now that might just beat out the toaster!
is it a head unit, or are there a couple 5" speakers at the bottom?
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Well it's all in the order of repurposing something. Even in sluckey's toaster repurposing his work is always orderly and neat down to the last wire. Mine is more on the order of borderline chaos.
This amp had good clean fender tone, a good measure of headroom and gets pretty loud. That's why I added the hot switch to add a little dirt. There is no high gain distortion there, just some good usable dirt overdrivish.
I've shown this amp on several amp forums and I think my favorite name someone tagged on it is "R2-D2"
To answer your question, it is a speaker-less amp head.
One of my favorite memorable experiences with this amp was a few years back I was playing with
the Slaughter Family Gospel group and we were playing at this little Church and I was setting it up and the bass player walked in and took a look and said "Why you want to play on something like that for??" He was actually really kind of mad and frustrated because he didn't want to be seen anywhere close to that amp. Hay I was really proud of it and thought it was kind of unique. Anyway after that I didn't take it out no more with that group out of respect for Jim the bass player. Platefire