Hell, why not go all the way and try an 833.
This is still a preamp you're talking about isn't it? Just getting caught up on many years of absence from intense audio activity. My living room is full of boxes of tubes trying to figure out what to build first. I have a few different pairs of DHTs from the 20's and 30's...and a few good OP xfmrs...still reading and learning. I have never played with DHTs, always been the more conventional 9 pin minis.
Really enjoying this discussion though, keep up the good work everyone.
Cheers
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Hell, why not go all the way and try an 833.
Really enjoying this discussion though, keep up the good work everyone.
No - the 845 idea was the output stage! Glad you're enjoying the thread. I want to build the 6C4C pre in filament bias ASAP!
I was just kidding but glad you're still checking out the thread. I have SO much to (re)learn, just figuring out filament bias right now. It's something I may have been familiar with back in the day but wasn't sure what it was called.
Anyway, now working my way thru the DHT amp thread, more good reading. I have a pretty good selection of DHTs for the power amp, 2A3, 801, 45, 811, 211, 805, 809, 833, probably some I'm forgetting about, I don't have nearly the selection of small signal DHTs but have a few pairs of 30, 27, UX-171, VR21 and 19. Would love to find some 01A, 10Y (although 801 really close) maybe 1H4G..I know I have a box of Loktals mixed with some old 4 and 5 pin tubes but I have searched for a few weeks and can't find it....pretty sure it's still in the shop but it's been -30C here for a week and the shop is -10 so searching for longer than 15 minutes at a time is tough. It's warming up now so I'll get back out there soon.
Cheers
Anyway, now working my way thru the DHT amp thread, more good reading. I have a pretty good selection of DHTs for the power amp, 2A3, 801, 45, 811, 211, 805, 809, 833, probably some I'm forgetting about, I don't have nearly the selection of small signal DHTs but have a few pairs of 30, 27, UX-171, VR21 and 19. Would love to find some 01A, 10Y (although 801 really close) maybe 1H4G..I know I have a box of Loktals mixed with some old 4 and 5 pin tubes but I have searched for a few weeks and can't find it....pretty sure it's still in the shop but it's been -30C here for a week and the shop is -10 so searching for longer than 15 minutes at a time is tough. It's warming up now so I'll get back out there soon.
Cheers
Well that's cool as I have both tube types and sockets and also some input xfmrs to try. As a retired broadcast engineer and crazy ham I have collected a LOT of stuff over the years and have a good selection of the 800 series of Hammonds. They are rated for +20dBm and 50-15K +/- .5dB, and probably better than that in reality. I have a couple of nice Allnic OP xfmrs as well from a 300B amp A5000 I think, which will be close enough for the 2A3, a bit overkill but I have them. Forgot I also have some 300Bs which are drivers for one of my commercial 805 amps, used as drivers for the 805, that thing scares me, it's over 100lbs and has great potential to kill the cat. It's in the spare room right now...along with the Levinson 332. That 805 amp just spanked the Levinson, no contest.
Anyways, on page 2 of the DHT amp thread, lots more reading ahead.
Cheers
PS speakers are Big Reds (Altec 604E) about 100dB/Wm so I don't need a ton of gain or power.
UX-171 or UX-171A?
If they are 171, I would find a way to use them.
Pretty special tube.
UX-171, no A. I'm going to have to dig out my old tube testers, although I doubt these will be listed. I'll first check heater continuity.
I'll post pics tomorrow, they still have stickers from our local radio shop, pretty cool.
Thanks for everyone's encouragement.
Cheers
Suppose, that you want to use three stage DHT amplifier: DHT VAS stage, x71 drive, 300B.
Ug peek of 300B let it be 75V.
The R loaded x71 gain is -about- 2.2.
VAS estimated stage output is 75/2.2 = 34.1V peek.
VAS estimated gain is 34.1/2.828= 12
Very few DH tube know this.
Possible VAS tubes: EML20/30 or the little problematic (high anode voltage, high impedance) 841.
You can use lower gain tubes (#26, 10Y/801 has about 8) with 1:2 SUT.
Well I was mistaken, the tubes I have are Westinghouse UX-171-A, and I can only find markings on one but they look identical inside and out. I put them on a 5V supply and both measure 240mA. Not sure of the sonic differences between the A and non A.
Here are a couple of pics. Heading out to the shop to see what else I have stashed away.
Cheers
Here are a couple of pics. Heading out to the shop to see what else I have stashed away.
Cheers
Replace resistor load with choke, gain is now 3.
75/3 = 25V peak, VAS gain required (2vRMS input) = 8.8
Use 01A, 12A, 26 etc.
The rule of the thumb designing tube power amp: the power tube nearly saturating than any previous stage.
If the x71 tube has -40V bias, the 25V peek input push 300B grid to A1 border (at -75V bias 150Vpp grid swing), and driver tube has enough headroom.
If the VAS stage has 8x gain (even CCS loaded 01a, #26 or 12a never achieve this) it hasn't enough gain to reach 25Vp at 2VRMS (2.828Vp) input.
With 1:2 SUT (or significantly higher gain tube) the VAS stage has sufficient gain with enough headroom.
If the x71 tube has -40V bias, the 25V peek input push 300B grid to A1 border (at -75V bias 150Vpp grid swing), and driver tube has enough headroom.
If the VAS stage has 8x gain (even CCS loaded 01a, #26 or 12a never achieve this) it hasn't enough gain to reach 25Vp at 2VRMS (2.828Vp) input.
With 1:2 SUT (or significantly higher gain tube) the VAS stage has sufficient gain with enough headroom.
You won't believe this, but I bought a whole lot of 10Y many years ago from a Canadian surplus dealer. I dare not even reveal the price, but let's say they were cheap.
You can buy them NOS from Langrex in the UK.