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900v ct PT - What to build? Suggestions please ;)
900v ct PT - What to build? Suggestions please ;)
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Old 14th January 2018, 01:02 AM   #1
OrbitalLex is offline OrbitalLex  United States
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Default 900v ct PT - What to build? Suggestions please ;)

I have a vintage Hammond Power Transformer with a 450-0-bt-450. I think I measured 50 something on the bias tap. A 5v pair and 6.3v pair. I don't know the current rating, but it's big enough to anchor an aircraft carrier, so I should be ok.

I have done many 5e3, jtm45, champ, Princeton, dumble clones. What can I do with this thing? Any suggestions? I wanted to do a 6G2 Princeton Reverb or similar, but I think this is too much.

Thanks for any ideas!

Chris
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Old 14th January 2018, 01:30 AM   #2
seppoa is offline seppoa  Sweden
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Well, depend on what you want to spend on output tubes and iron. But one suggestion would be EL34 PP, nice tubes that can do much with the about 630 volts that the DC after rectificaton with SS diodes would give. Have not looked up the figures, but this would get you a lot more than 50 watts, with an OPT of about 5-6 kohms P-P.

BTW, if your question is about guitar amps, then this is not the right forum. Here we discuss HiFi

Last edited by seppoa; 14th January 2018 at 01:38 AM.
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Old 14th January 2018, 01:41 AM   #3
OrbitalLex is offline OrbitalLex  United States
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Well, my initial idea was guitar related. I recently built a stereo el84 p-p amp. Sounded amazing and was a lot of fun. Maybe that's the direction I should go in. Would be nice to have tube amp in the office
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Old 14th January 2018, 01:43 AM   #4
Lingwendil is offline Lingwendil  United States
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900v ct PT - What to build? Suggestions please ;)
6L6GC, EL34, or 6550 would be good outputs for that sort of voltage.
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Old 14th January 2018, 02:06 AM   #5
PRR is offline PRR  United States
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Hammond hasn't changed their parts since the 1950s. Try to look it up. Weigh it and find one of the same heft. Knowing the current will set some outer limits what is practical. But if it really came off an aircraft carrier, it may be for a kiloWatt radio ham rig.

Several tubes will stand >600V on plates. Very very few are rated for near that much on screens. Since screen current is very variable we can not take a large drop in a dumb resistor. True, even back in the 1970s it was possible to rig a TV transistor and 300V Zener string (selected 1N914) as a solid G2 supply.
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Old 14th January 2018, 02:34 AM   #6
seppoa is offline seppoa  Sweden
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Quote:
Would be nice to have tube amp in the office
That would be nice But also that would be much to much for having for background music during work. No, that transformer is for doing heavier work, at high volumes
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Old 14th January 2018, 02:41 AM   #7
OrbitalLex is offline OrbitalLex  United States
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The bells were painted, so I need to remove some of that to get the code. I'm leaning towards a dual el34 p/p rig of some sort. I have a mess of 5ar4 and 5u4 recs laying about.
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Old 14th January 2018, 02:48 AM   #8
seppoa is offline seppoa  Sweden
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Quote:
300V Zener string (selected 1N914) as a solid G2 supply.
That was interesting. But how many 1N914 was needed to find the right ones? And is 1N4148, which is the common equivalent, equally usable?
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Old 14th January 2018, 03:27 AM   #9
Eli Duttman is online now Eli Duttman  United States
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Quote:
Hammond hasn't changed their parts since the 1950s.
That concept and the OP's 450-0-450 doesn't "jive" with Hammond's product chart. The 278X and 279X come close. Neither of those items will produce the current needed to support a stereoblock using EL34s or 6L6GCs, when cap. I/P filtration is employed. A possible stereoblock using a 278X would employ PPP 6Π14Π-EB (6p14p-ev), AKA EL84M, "finals" and a SS rectified choke I/P filter B+ PSU. Being able to access the full VA capability of the power trafo contributes mightily to the cause. Voltage multiply the 5 VAC winding to derive the bias (C-) supply.
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Old 14th January 2018, 03:49 AM   #10
daqvin_carter is offline daqvin_carter  United States
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If you can weigh the transformer and also measure dc resistance of each winding, we should be able to better guess current ratings based on other transformers.

Also, remember when measuring the HV winding, you can get flyback voltage spikes if you are holding the windings in your hands while attaching the ohmmeter leads. It is sometimes a little fun or maybe to avoid.
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