I have been playing with 300B, 2A3 kind of DHTs for the last decade and half. Great tubes great SE amps. But I thought it's time to move on.
SE amp with TT filament at the output at tight budget was a challenge. Once you exceed 420/430volt B+ and 80/90ma total current things become complicated which eventually turns into costly project. For hot countries another important aspect is the heat an amp produces. All the big tubes also run hot of-course.
I am also happy that everybody participated this thread joyfully and no fighting happened. I joined this forum in 2004 and I have tasted many bad examples. The objective of the forum is sharing and helping each other not other way round.
I think many of us who have played enough with DHTs now can start with budget low heat TT projects considering HY69 at the output.
I salute Bandersnatch for sending the tubes to L0rdGwyn, I also salute L0rdGwyn for tracing the triode curves. Much appreciated.
I need few good source to buy HY 69 please help!
Regards
SE amp with TT filament at the output at tight budget was a challenge. Once you exceed 420/430volt B+ and 80/90ma total current things become complicated which eventually turns into costly project. For hot countries another important aspect is the heat an amp produces. All the big tubes also run hot of-course.
I am also happy that everybody participated this thread joyfully and no fighting happened. I joined this forum in 2004 and I have tasted many bad examples. The objective of the forum is sharing and helping each other not other way round.
I think many of us who have played enough with DHTs now can start with budget low heat TT projects considering HY69 at the output.
I salute Bandersnatch for sending the tubes to L0rdGwyn, I also salute L0rdGwyn for tracing the triode curves. Much appreciated.
I need few good source to buy HY 69 please help!
Regards
L0rdGwyn...I am very interested about your 801A A2 project. Please keep us posted.
I have a pair of VT25, how much watt it can make with 5K load in A2 you think.
Regards
I have a pair of VT25, how much watt it can make with 5K load in A2 you think.
Regards
Me uses 6N7G>EL34>845 operating @ 480v B+ and 65mA.
Using cheap James 6123H on 5K6. Low watter with good bass 😀
But, of-course the final link is a 101dB speakers.
zekk.....I use James OPT and they are not bad, not cheap either.
Anyways self bias or auto bias? I heard that 845 at low voltage/low current is lazy sounding if self biased?
Regards
Anyways self bias or auto bias? I heard that 845 at low voltage/low current is lazy sounding if self biased?
Regards
James 6123H was bought 22yrs ago when I first started diy tube amp. From Taiwan by the founder of James transformers. It've gone thru numerous tubes and configuration during my trial and error journey.
Fixed bias @ -54v at grid of 845.
I'm an old rocker, grew up during the rolling stone era, slow rock music is my cup of tea.
Before this amp, I used IPC 1026 cinema amp, and I've the tendency to crank-up the volumn to whack my neighbours! My speakers are Altec 604-E in 9cu.ft enclosure.
Fixed bias @ -54v at grid of 845.
I'm an old rocker, grew up during the rolling stone era, slow rock music is my cup of tea.
Before this amp, I used IPC 1026 cinema amp, and I've the tendency to crank-up the volumn to whack my neighbours! My speakers are Altec 604-E in 9cu.ft enclosure.
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Type 211 can be run at these "low" voltages too. Higher mu than type 845, so less B+ loss than with type 845 when cathode resistor biased. Not an amazing power output but extremely clean idling at whatever current your output transformer can handle reasonably linearly. This region of operation is the most linear available, at the penalty of peak output - as Zekk said, the secret sauce is speaker sensitivity.
All good fortune,
Chris
All good fortune,
Chris
Yes indeed; many thanks to Douglas and L0rdGwyn for the triode plate curves. I never expected them to look so good. That really presents a problem! I love the HY69 in Pentode mode but now I am curious about triode...
I have already a 300B amp with a 5k:16 output transformer. I might have to try a SE HY69.
Minhaj: PM me about the HY69 tubes. I trolled all the online dealers a year or so ago and bought up the few available.
yeah, that is nuts alright. I am quite fond of one of its relatives, the HK257. I do think it is time to build an amp around triode finals. Going in off the high dive into the deepest end. Zero bias, and cathode drive on HY51A finals. Should be quite enough to tax the limits of an M4-stacked S-265-Q output TX. I will need an amp to drive them...something like +/- 40V of signal input into a 300 Ohm load( each cathode ).
IMO, better a heavy but constant load vs a discontinuity when the grid goes positive.
cheers,
Douglas
Grover's circuit? Me too. I'm running a 900+ B+, but I was thinking I could probably see how it worked at lower voltage by just hooking the B+2 to the 845 plates. Though the choke I'm using there wouldn't like that load very much.
I don't see why one would need a big expensive OPT to make something that works. At low wattage, even the popular old Sony R2R transformers seem like candidates.
The Shuguang 845s are cheap enough new, it is hard to find the suckers used. I found a barely used pair for <$100USD. But even new, they are only a little more than half what the Shuggy 300bs cost.
I'd be curious to see how a 12V SMPS/laptop supply would work on the heaters with some additional filtering. Or maybe bits repurposed from a car battery charger, either linear or switch mode.
So, while my 845 has some more expensive bits (found by accident, mind you), it is a bit baffling to me that lower buck lower voltage versions aren't popular projects!
Paul
Douglas,
Have you seen my 826 A2 SE amp? Corona: An Ultra-Low Distortion A2 DHT SE Amp Prototype
Not sure if you are averse to using a mosfet to drive the grid, but it works pretty well.
I do not have a project page. All I can say is transformer rectified filament voltage.
Two 6Sn7 gain stages. Battery bias for -18 volts and the rest is self bias through 12 volt LED strips. I would have to open it up to get a schematic.
SE Amp with Thoriated Tungsten output tube
Just to put some more meat on the 'John Steward challenge' (post 135),
🙂
Just to put some more meat on the 'John Steward challenge' (post 135),
🙂
No I had not. I don't believe a source follower will take very well to a step change in load. Don't want to use a power tube that needs grid current flowing all the time either. I'm at the limit with an HY51A with plate resistance about equal to load resistance. Unfortunately there is not a version with half the gain...if there was they would be so hard to find it would seem 842's lived in the nickel a tube box.
Second, the amplifier in the FB path? No way man. Not going to put them in series with an amp either( regulating B+ ).
cheers,
Douglas
Hi Paul..Yes, it's Grover's design which surfaced in SET Asylum but minus operating voltages. Took a gamble, did lots of detective works, to come out with my own operating parameters. I'm no EE but just a retired off-shore piping engrg. Common sense and passion will lead the way. Cheers!
I finished a single channel of my 801A A2 design with some preliminary measurements here: Corona: An Ultra-Low Distortion A2 DHT SE Amp Prototype
Ahh the HK257, think I linked some 4E27A triode curves earlier in this thread, not traced by me, they are very linear in A1. HY51A, that's an oddball, impressive curves, looks well-suited for 0Vg bias, I will keep an eye out for your design 😀
Will be putting your tubes back in the mail later today, thanks for sending them.
Ahh the HK257, think I linked some 4E27A triode curves earlier in this thread, not traced by me, they are very linear in A1. HY51A, that's an oddball, impressive curves, looks well-suited for 0Vg bias, I will keep an eye out for your design 😀
Will be putting your tubes back in the mail later today, thanks for sending them.
We all have our preferences. That's what makes this hobby fun, doing it your own way.
But I'm curious why you think the step change in load would be a problem for the source follower. Did you have some results that point to it being a problem? I'm not seeing any high-order harmonics even at high output levels.
The "amplifier" in the FB path is just a p-channel follower that prevents AC plate/screen currents in the input stage from spoiling the plate voltage sample. It just buffers, no amplification takes place. It results in a very substantial reduction in distortion.
Regulating B+ wouldn't be necessary in a push-pull amp, which is what you are planning to make, right?