Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: sonicdealthmonkey on March 09, 2018, 03:23:26 pm
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Greetings,
I know there are a couple previous threads about doing an HRDX point to point rebuild/rebirth, but I'm very new at this and I need a bit more detail before I plunge in on this. I'm on a budget, so I'm looking to do a 6L6 AB763 single channel build using as many of my existing parts as I can. Everything is in great shape (tubes, speaker, transformers, tank, etc.) but the PCB is garbage. I'm also considering a 6L6 5F6A build since it's a bit simpler, but I'm not sure if that's appropriate in the 112 cab.
I'm unsure of a couple of things:
Can I reuse things like:
-pots
-transfomers
-reverb tank
What are the tonal differences between circuits (apart from reveb and vib)?
Has anyone made custom circuit board for the heavier caps (for vertical mounting)?
If anyone else has done this end to end, I'd love to read up on it before I start ordering parts. I'm definitely a novice at this, I've only had a wee bit of exposure to this type of work back when I was in the Army in the late 90's, so I'm definitely looking for something I can just read and follow.
Thanks
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Tubes, transformers, and speaker are about the only things you can reuse. The reverb tank is not compatible with a tube circuit. Pots are pc mounted.
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Tubes, transformers, and speaker are about the only things you can reuse. The reverb tank is not compatible with a tube circuit. Pots are pc mounted.
Thanks, that'll probably cross off AB763.
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I too have a HRD on the fritz for the umpteenth time and have been avoiding a rebuild.
Anyway note that you can use the existing tank with a Traynor style cap driven reverb circuit. But it's not as lush as Fender style. Or you could SS drive the reverb tank or use a reverb chip.
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I did a conversion last year, great size chassis and cabinet to work with.
Use transformers, cab, speaker, and tubes if you like.
Make new boards and populate.
No reverb put a treble cut pot in reverb spot.
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Awesome feedback, thanks guys. MFowler, thanks for the PDFs, very very helpful.
Just one more question. I saw videos for the Princeton Reverb project, the tone is amazing. Can I get away withing re-using my transformers for that circuit?
Again, thanks. This has all been very helpful.
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Yes. But you'll need to build a different bias supply.
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I have a question about my build that I'm hoping the community could answer. Here's my power trans (stock Hot Rod Deluxe):
https://drive.google.com/open?id=1QGkrpLKIoDMr_dY462N5ew2tTbzqxbkT
Here's what the diagram says:
https://drive.google.com/open?id=1wRP8yXrvNBlCfEba1pOmB_SK_q15F6LR
I'm confused about I am to connect the bias tap and ground. Could someone dumb this down for me?
Thanks
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I did a conversion last year, great size chassis and cabinet to work with.
Use transformers, cab, speaker, and tubes if you like.
Make new boards and populate.
No reverb put a treble cut pot in reverb spot.
What tube sockets did you use?
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Connect the brown wire to ground. Connect the other brown wire to the bias circuit.
We can't see your google pics without signing in.
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I used Belton tube sockets.
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> We can't see your google pics without signing in.
It looks to me like he is mixing a CT plan with a FWB plan?? That may not be happy.
(Don't know why he points to a Hoffman website diagram hosted in his Google.)
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It looks to me like he is mixing a CT plan with a FWB plan?? That may not be happy.
I agree. Not gonna work. Just copy the power supply from Hoffman's Blues Junior conversion.
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> We can't see your google pics without signing in.
It looks to me like he is mixing a CT plan with a FWB plan?? That may not be happy.
(Don't know why he points to a Hoffman website diagram hosted in his Google.)
Thanks for reposting these. I couldn't figure it out.
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It looks to me like he is mixing a CT plan with a FWB plan?? That may not be happy.
I agree. Not gonna work. Just copy the power supply from Hoffman's Blues Junior conversion.
I'm really just using this plan:
http://el34world.com/Hoffman/files/Hoffman_5F6A.pdf
I thought I could reuse the stock power trans. Is that not the case?
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I'm really just using this plan:
http://el34world.com/Hoffman/files/Hoffman_5F6A.pdf
I thought I could reuse the stock power trans. Is that not the case?
You cannot use that PT with the Hoffman 5F6A.
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I'm not following the whole project. But seems to me if you want to use the stock HR PT for another build with similar tubes, the power supply should be stolen from the HR's plan.
Seems to be 4 diodes instead of 2 (so not the bottle rectifier). Has the bias supply mentioned. Also has feeds for switching and op-amps which you don't need.
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That's correct has to use the HRDX schematic to use the original PT see my photo above showing full wave bridge rectifier on board.
Mark
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thanks guys. I went ahead and ordered the correct PT. It's the path of least resistance for me to get this done. I appreciate all the help.
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I'm mostly done my build. I do have one thing that I cannot figure out, so I'm hoping someone can point me in the right direction. The treble pot seems to be controlling volume. If it's at the low stop, no volume; high stop is very high volume. For now, I'm leaving it at 3/4 and using the actual volume pot(s) to find the volume/tone I'm looking for. I've gone over the diagram a number of times, the pot looks to be wired up correctly. Any ideas?
EDIT: 5F6A circuit, for clarification sake
http://el34world.com/Hoffman/files/Hoffman_5F6A.pdf (http://el34world.com/Hoffman/files/Hoffman_5F6A.pdf)
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You may have a normal, alternative TS wiring; whereby turning the tone controls to -0- kills volume. E.g., go to: http://hotroddiy.com/; click on The Articles; click on James E Vanden Berg Mods, The; Go to p. 4 middle.
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I too have a HRD on the fritz for the umpteenth time and have been avoiding a rebuild.
Anyway note that you can use the existing tank with a Traynor style cap driven reverb circuit. But it's not as lush as Fender style. Or you could SS drive the reverb tank or use a reverb chip.
i have had one of those in my shop twice. the third time he wanted to bring it back, i told him i wouldn't work on another PCB equipped amp. period. that's my policy from now on, unless the PCB was designed by me or someone i know. fender HRD seem to nothing but a headache for their owners. another customer has a marshall DSL2000 coming back for the third and last time - what a *&^%ing nightmare of an amp to work on that one.
+1 on the parts to salvage to build AB763 with cap coupled reverb driver. keep as much as you can out of the landfill.
--pete
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You should see the TSL 2000. After I seen the inside i quickly sold it.