I have a pair of Hammond 1627SEA output transformers and even the power supply bits for a tube amplifier (parallel 1625s) that went nowhere. It was a complicated affair with regulated screens, plate-to-plate feedback, and video pentode drivers where I ended up almost completing one monoblock.
Looking for something a little simpler, perhaps stereo build, and can make use of these big output transformers. Any single output tube that matches up nicely with a relatively low 2500 ohm output transformer?
Looking for something a little simpler, perhaps stereo build, and can make use of these big output transformers. Any single output tube that matches up nicely with a relatively low 2500 ohm output transformer?
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Well.....
There was a triode wired SE EL34 circuit on the Angela Instruments site a few years ago that used a small Hammond at 2500 ohms, though that seems a bit low. The SSE by George at Tubelab.com uses an EL34 but with a 5K transformer.
The big trans you have would likely support a parallel SE EL34 (or 6550) and using a pentode you could run it Ultralinear using the tap on the Hammond primary.
Steve
There was a triode wired SE EL34 circuit on the Angela Instruments site a few years ago that used a small Hammond at 2500 ohms, though that seems a bit low. The SSE by George at Tubelab.com uses an EL34 but with a 5K transformer.
The big trans you have would likely support a parallel SE EL34 (or 6550) and using a pentode you could run it Ultralinear using the tap on the Hammond primary.
Steve
6P45S triode strapped would work nicely. Say 300-320V B+ with about 120ma or so? Fixed bias, roughly -60 - -65V so you will need about 60 volts of drive but that's not hard.
Edit: Check this thread for the guy who thought of it before I did... D3A - 6P45S/El519 SE "The staircase" my first h-end amplifier.
Edit: Check this thread for the guy who thought of it before I did... D3A - 6P45S/El519 SE "The staircase" my first h-end amplifier.
According to this 300B operating conditions chart, 350 V. on the plate and -74 V. on the grid should work pretty darned well.
Plenty of heft in the O/P "iron" suggests that a DC coupled MOSFET driver and a little A2 action would be feasible.
Plenty of heft in the O/P "iron" suggests that a DC coupled MOSFET driver and a little A2 action would be feasible.
To work to the limits you paid for:
400V plate-cathode
160mA plate current
64 Watts plate dissipation(!!)
Perhaps 25 Watts Audio out with good pentodes
Perhaps 16 Watts with very good triode(s)
There is no obvious tube complement for this. Two 300B is too costly to think about. Two 6550/KT88 will stand the strain easily, and drive easy, but a lot of bottle for a mere 25 Watts. One KT120 may carry the load but I am always dubious about building for a single-source tube of no proven popularity.
400V plate-cathode
160mA plate current
64 Watts plate dissipation(!!)
Perhaps 25 Watts Audio out with good pentodes
Perhaps 16 Watts with very good triode(s)
There is no obvious tube complement for this. Two 300B is too costly to think about. Two 6550/KT88 will stand the strain easily, and drive easy, but a lot of bottle for a mere 25 Watts. One KT120 may carry the load but I am always dubious about building for a single-source tube of no proven popularity.
Why did you abandon the original plan? Overly complicated? Maybe build something more basic using the same tubes.
I'm looking at one BIG TV sweep tube like a 36LW6 driven by a TV video or IF amplifier pentode with plate to plate feedback and regulated screen supplies.....sound familiar? Preliminary testing saturated a Transcendar 3K OPT that was intended for 300B's at about 10 to 20 watts depending on test frequency.
I have a pair of Hammond 1628SEA's (5 K ohm) from a SSE test build about a dozen years ago. I used Edcors in the final amp build and the test amp was stripped for parts when I had to move everything 1200 miles. I plan on running an 8 ohm load on the 16 ohm tap for a 2500 ohm load on the tube. I may also try the same amp on 5K, but the B+ would need to be in the 600+ volt range to get 30+ watts.
The SSE would make about 14 watts in UL mode with a 6550 or KT88 on 460 volts and a 5K OPT. It would make almost 20 if I remember right when the transformer was mis-loaded to reflect 2500 ohms to the tube. It definitely did not sound as good, especially in the bass region, so I left it at 5K.
I eventually put the big 5K Edcors into the real amp build because they sounded better, and made about a watt more power than the Hammonds.
You could try putting an 8 ohm load on the 4 ohm tap to make your 2500 ohm Hammond look like a 5K OPT, then there are plenty of tube choices.
much appreciated, everyone. Lots of food for thought.
As to why I never finished the second one - ran into stability issues that I could never track down due to my current lack of test gear (which is another story). So the amps have been sitting on the shelf as a constant reminder that they aren't done!
As to why I never finished the second one - ran into stability issues that I could never track down due to my current lack of test gear (which is another story). So the amps have been sitting on the shelf as a constant reminder that they aren't done!
If that 11 lb. 2.5k transformer is anything like their 11 lb. 5k transformer,
Do Not apply negative feedback.
The 5k version has the very worst high frequency roll off, phase response, distributed capacitance, and leakage reactance I have ever seen on any transformer.
In its defense, the 5k transformer had the very best low frequency response I have ever seen for an SE transformer.
My test equipment at that time only went down to 10Hz, and the transformer was not even close to approaching 1 dB down there.
Do Not apply negative feedback.
The 5k version has the very worst high frequency roll off, phase response, distributed capacitance, and leakage reactance I have ever seen on any transformer.
In its defense, the 5k transformer had the very best low frequency response I have ever seen for an SE transformer.
My test equipment at that time only went down to 10Hz, and the transformer was not even close to approaching 1 dB down there.
I have a 4D32 (https://frank.pocnet.net/sheets/201/4/4D32.pdf) ultralinear on the breadboard with that OPT right now. 16 watts @ 5% THD, 400V B+ (yes I know that is pushing the G2 rating a little). Or 10 watts in triode if I remember right.
Not real low distortion - maybe 0.8% @ 1W.
Using a single 12GH7 triode wired with a CCS load and a small amount of overall NFB.
Pete
Not real low distortion - maybe 0.8% @ 1W.
Using a single 12GH7 triode wired with a CCS load and a small amount of overall NFB.
Pete
Attachments
I don't have any 2500 ohm OPT's as large as the 1627SEA....yet. I did wire my 1628SEA's (5Kohm) with the 8 ohm load on the 16 ohm tap to reflect a 2500 ohm load on the tubes in the hot seat. I can report that it is possible to squeeze 40 watts out of a single tube in this manner. I might have ignored a few critical tube specs though.
20 watts from a 36LW6 is possible without melting anything. I have used a new topology for these experiments that is the result of nearly 10 years of blowing stuff up, backing up and trying again. Well over 250 watts from a pair of 36LW6's in push pull is also possible.
Unfortunately my experiments and data have become scattered in several threads. I will try to get it all in one place in the coming weeks.
UNSET is coming?
https://www.diyaudio.com/forums/tub...sing-mosfet-ultralinear-feed.html#post6267790
If UNSET and the RCA50W Had a Baby
20 watts from a 36LW6 is possible without melting anything. I have used a new topology for these experiments that is the result of nearly 10 years of blowing stuff up, backing up and trying again. Well over 250 watts from a pair of 36LW6's in push pull is also possible.
Unfortunately my experiments and data have become scattered in several threads. I will try to get it all in one place in the coming weeks.
UNSET is coming?
https://www.diyaudio.com/forums/tub...sing-mosfet-ultralinear-feed.html#post6267790
If UNSET and the RCA50W Had a Baby
What about 6P43P in triode? Is this OPT big enough to handle a parallel-pair of those? The Ip of the two in parallel would be 90mA, with about 250V plate-cathode (Pdiss = 11.25W per triode.) That should make reasonable power for a single-ended triode amp, no? It would be nice and easy to drive.
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