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Old 22nd July 2011, 09:16 PM   #1
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Join Date: Jul 2011
Default My first HiFi project

Hi,

I have some stuff from guitar amp like :

- one pt for Marshall Jtm100 (490Vdc, 6.3 heaters) and
- one for Jmp100 (490Vdc, 100V bias trap, 6.3 heater)
- 3H choke
- some quads of kt66, el34, 5881 and ecc81, 82, 83, 88
- many components like Allen resistors, Ars caps...

I would like to use one of my PT to minimize the cost so

what kind of amp can i do with these parts?

Thanks guys,
J4zzy
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Old 22nd July 2011, 09:24 PM   #2
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Location: Minneapolis, Minnesota, USA
Do you have experience working aroun high/lethal voltage?

Mike
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Old 22nd July 2011, 09:44 PM   #3
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hi Michael,

Yes i've built my own ac30 top boost and a Marshall Jtm45-100 replica !



Do you have any idea?

Regards.
J4zzy
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Old 22nd July 2011, 11:39 PM   #4
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I'm not terribly familiar with guitar amps,but I suspect you could pull off some kind of PP EL34/KT66 amp easily enough with that power iron.
You'll have to find some suitable output transformers.

Personally,I'd probably use the JMP100 transformer,just because it has a tap for a fixed-bias supply (could also be useful for CCS's,etc.).
If you decide to go with self/cathode-biasing,you might not need the tap,and either transformer should work nicely.

Build up a CLC PSU,and a basic Push-Pull output stage. Triode/pentode/UL operation is up to you,and your choice of output transformers.
Use a LTP with a CCS in the tail for the driver/PI,and away you go.
You can tweak/refine it from there,once you get the basic 'skeleton' circuit worked out and operating suitably.
Depending on the topology and so on,I'd think it could make a cool 30+W per channel.

Duncan's PSUDII will help you model/design the power supply..
PSUD2
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Old 22nd July 2011, 11:59 PM   #5
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Location: Minneapolis, Minnesota, USA
I'm not really the right person to say much about valves in a HiFi application, I messed around some with guitar amps in my long lost youth, but I'm pretty much sand-state oriented. When I saw your "My first HiFi project" heading, I was concerned for your safety, it always makes me nervous to think about inexperienced noobs poking around high voltages. I'll leave build recommendations to others here who, no-doubt, know a lot more about valves than I do.
Good luck, and safety first.

Mike
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Old 23rd July 2011, 12:13 AM   #6
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YES. Do be careful!
That 490V B+ will hurt at the very least,and is FATAL in the worst case.
Always observe proper safety precautions when working with tube/valve equipment.

Safety Practices, General and Ultra-High Voltage
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Old 23rd July 2011, 08:39 AM   #7
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Thanks Digital, i'm going to think about this way !

Don't worry guys i'm electro technician and i'm enable to work with three phase HT.

Regards.
J4zzy
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Old 23rd July 2011, 04:21 PM   #8
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You are fortunate in that your PT is from a PPP amp so you should have ample current for stereo PP if you like. Of course you could do SE if you wanted to. Use which ever set of outputs you prefer as they are all well respected tubes of about the same capabilities give or take.

You can do Triode, UL, or Pentode mode depending on how much power you want, what kind of feedback you are willing to use, and how complex you want to get. For triode or UL mode you might be able to use no FB at all or some local FB. In pentode mode you will probably end up having to use some global FB I suspect.

You have a nice selection of preamp tubes there too. I personally would save the nice ECC88s for a cascode input stage for the phono preamp and use the ECC81/12AT7 as the VAS and PI for the power amp. If you do some searching you will find a lot of PP amps using 12AT7 and the 6L6 class of tubes in PP so there are a lot of designs out there to dissect and study.

Personally I would be tempted to go with 12AT7 VAS DC coupled to 12AT7 Cathodyne with KT66 in UL with local plate to plate feedback on the output stage. If you wanted to try pentode mode it would be a pretty simple thing to run a global loop back to the cathode of the VAS. If you found the 12AT7 laking in gain for the global feedback situation you could try redoing the VAS for the 12AX7 equivalent (ECC83 IIRC).

You could go LTP but then you have to decide whether you want to dick around with a CCS or try to use the B+ you have with just a big resistor. I don't think that your 3H choke has anywhere near enough inductance to use it for a choke tail pair otherwise that would be a fun variation to try.

You could use the choke in the PS as a CLC filter for the plate supply.

That is a nice stash of parts and makes for almost unlimited options. Best of luck.
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