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Old 18th January 2013, 04:24 PM   #201
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Quote:
I suppose I have one question.. Should the 10m45's be hot?
The higher (more negative) your negative bias supply is, the hotter the cathode 10M45 (U1) will be, since it dissipates most of it as heat. The other 10M45's are fed by the board B+, so their temperature depends on that voltage.

The life expectancy of sand state critters is affected by their operating temperature, with zero lifetime at around 150C internal die temperature. So, if they are too hot to touch, I would look into a bigger heatsink. You can also reduce their dissipation by adding a resistor in series with the drain (anode) lead. I did this on the SSE board. Some say the added resistor improves the sound, but I never heard a difference when I jumpered the resistors.

My little red board has the same small heat sinks that I use on the SSE attached to each 10M45. U2 starts smoking when the B+ gets cranked to 600 volts, so I now have 2 heat sinks on that one. They are still much too hot for long term reliability.

Quote:
it appears that the 7403/3D21WB works very well here...Any particular brand?...Where they are available?
I have seen Bendix, and Cetron with a metal base, and "USN" (US Navy, no clue who actually made it) with a brown phenolic base. The 5 new ones that I bought had no name at all, but have the newer metal base. All have Bendix style ceramic spacers instead of mica with metal spring clamps touching the glass.

They are hard to find, so you just have to check with the tube sellers that you deal with. VaccumTubes.net has them listed at $35 each, but I don't know if they actually have any.
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Old 18th January 2013, 10:12 PM   #202
wicked1 is offline wicked1  United States
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Originally Posted by pso View Post
Hi, it appears that the 7403/3D21WB works very well here.

Any particular brand?

Where they are available?
I got lucky and found some in a bin at a local electronics store.. ebay claimed to have a bunch, but when I further inquired about them, they were just B's, not WB's.
I did see them at one or two online vendors, as tubelab mentioned, but they were more expensive than kt-88's, so don't bother.

Thank you, tubelab.. as always...

Last edited by wicked1; 18th January 2013 at 10:15 PM.
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Old 11th February 2013, 01:14 AM   #203
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Click the image to open in full size.

Finally posted details about the PPP 807 amp (using this driver) on the web page. Still a few things missing (like a BOM) but most of the info is there:

"807" Push-Pull amp
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Old 11th February 2013, 01:54 AM   #204
Cassiel is offline Cassiel  Libya
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Well, that's a nice pic. Amp looks pretty classic. I like it, specially the chassis color.
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Old 11th February 2013, 02:44 AM   #205
wicked1 is offline wicked1  United States
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Looks good!
I finally got all the bugs worked out of mine (regulator issues) and took apart one channel this weekend to start chassis work. It's sad to have them disassembled for a while.
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Old 15th February 2013, 12:46 AM   #206
davefl is offline davefl  United States
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Quote:
Originally Posted by pmillett View Post

Finally posted details about the PPP 807 amp (using this driver) on the web page. Still a few things missing (like a BOM) but most of the info is there:

"807" Push-Pull amp
I'm thinking of asking Edcor to make a power transformer for this amp with multiple taps for B+. Something that would be more "universal" for different output tubes or to drive the 807's harder. Any recommendations or requests for voltages?
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Old 15th February 2013, 01:24 PM   #207
wicked1 is offline wicked1  United States
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I've found this classictone tx relatively versatile. Under 500v w/ the 120v taps, and about 600 w/ the 110v taps. The heater is unfortunately either a little under voltage or a little over voltage, w/ my mains. Personally, if I could have one more output, it would be lower so I could use tubes that like 350ish volts.
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Old 16th February 2013, 12:28 AM   #208
davefl is offline davefl  United States
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I have a couple questions off to Edcor about the transformer. I suspect 4 or 5 taps won't cost much more than 2, but we'll see. I just hope the whole thing isn't prohibitively expensive. I'll let you know what I hear.
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Old 25th February 2013, 02:33 AM   #209
davefl is offline davefl  United States
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Heard back from Edcor the other day. Apparently they won't make a drop-in replacement for the Classic Tone pwr xfmr Pete used, seems it's an odd size for them. They can make a similar vertically oriented xfmr, but they only like to fit 2 taps through the hole in the end bell. Since the Classic Tone has the higher voltages covered pretty well, I think I'll go with 350v and something lower as wicked1 suggested. Thinking 275v. Any comments?

Also, they said it would be just under $70 per unit with 120/240 v primaries and secondaries like the Classic Tone.
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Old 1st March 2013, 03:41 AM   #210
AJT is offline AJT  Philippines
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Quote:
I suppose I have one question.. Should the 10m45's be hot? As in, turn the amp off, let it discharge for a few minutes, and I still can't touch the heatsink for more than a second. Someone else has my IR thermometer right now, so I can't be more precise than that...
what i do in this case is to add a series resistor so that the power dissipated by the 10m45's can be shared with the power resistor....
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