Paul, I am curious about the large tube as I have never seen anything like it. Can you provide some detail about it as I am in the dark.
More Amp Construction
- Thread starter paul_b
- Start date
I was just wondering the same thing
Seems odd the way the tubes were soldered directly. Old school?
New school:
5703, Tube 5703; Röhre 5703 ID5878, Triode, vacuum | Radiomuseum.org
Tube 5703 or Röhre 5703 ID5878, Triode, vacuum, and UHF shown. Radio tubes are valves.
www.radiomuseum.org
A lot of those sub miniature tubes were soldered into missile guidance systems where space and weight were at a premium.
The really big amp uses an 833 triode, which is a very beefy transmitting triode. It would hypothetically be possible to get 140W out of one of these, but transformer size limitations have me aiming a bit lower than that.
The really big amp uses an 833 triode, which is a very beefy transmitting triode. It would hypothetically be possible to get 140W out of one of these, but transformer size limitations have me aiming a bit lower than that.
Tubemonger has taken flying lead versions of some popular preamp tubes and created coinbase versions of them. I bought a pair of CV4033 and they are superb.
Beautiful! Is that a ladder attenuator?
That preamp is getting the JV-8 attenuator module, which is a relay based attenuator setup that switches in and out resistors to provide the desired attenuation. I would not call it a ladder attenuator, though Lite Audio makes some modules that are true ladder attenuators (but they are gigantic!).
I like that whole amp can sit on the tube socket. ;-) At least it looks that way...
The top and bottom panels are attached in the middle with some beefy aluminum standoffs since things are a little heavy.
This one is up and running but number two needs a redo on the top panel from SendCutSend, so it's back to preamps and an electrostatic headphone amp.
This one is up and running but number two needs a redo on the top panel from SendCutSend, so it's back to preamps and an electrostatic headphone amp.
I get asked somewhat frequently why I don't make many 845 amps. To me, the 845 delivers relatively little power off a ton of voltage through an output transformer that's difficult to source and make properly, and that's just too long of a list of disadvantages. I have long suggested aiming much higher if you're going to bother with a 1kV power supply in the first place, and this is what I landed on:
I finally got one of these on the bench today and found that I achieved my goal of 75+ watts and made it all the way to 88W! This circuit uses the same topology that I have used in other class A2 amplifiers, which is a pentode front end (807) driving a beefy choke loaded cathode follower (6HS5) that's directly coupled to the output tube (833). I also employed a single damper diode (6KD3) to slow the ramp-up of the high voltage supply, and of course I added a high voltage fuse between the rectifier bridge and the rest of the amp for a little additional safety which is a precaution I don't usually take.
Inside you can see there isn't a whole lot going on in this amp. The SMPS filament supply covers up a lot of the power transformer wiring and some of the high voltage bridge rectifier, as well as a basic 6V DC power supply I added in to heat the 807 (they aren't known for being the quietest tube ever). All the white wire is 15kV rated (and the rest of the smaller PVC jacketed wires are fine up to 1kV), and the single terminals are good for 6kV. The bottom panel holds a very quiet 120mm 12V fan that runs off the 10V filament supply and fires right up through the hole onto the base of the 833, so there's some force air cooling blowing out the top of the glass chimney. I have added a balanced input that can be hooked up to an octal transformer for added flexibility.
I spoke with Monolith about an output transformer when I had this idea and managed to get something made that exceeds my expectations and wasn't overly punishing to my wallet, as their dedicated 833 output transformer is 12K (I needed 5K), amorphous cored (more material required to reach the specified operating level), and a dual C core (possibly leaving a lot of extra space in the can), I asked for an EI core customized unit, and they delivered nicely! While I see 88W at 1kHz/10% THD and 87W at 5% THD, that power only drops to 81W at 10% THD/35Hz, which is above my expectations. The amp is -3dB at 11Hz and shows less than 1dB of drop at 20kHz, which I expected since I had tested one of these previously in a different circuit.
The power transformer and chokes in this amp could be sourced from Hammond, so that wasn't a tough choice, and I went with a nice selection of Mundorf caps and fancy resistors from Parts Connexion where they would work properly. The plate-to-plate feedback resistor in this amp gets a horrendous amount of abuse, and luckily there was a 4.5kV rated Caddock available that worked appropriately.
I will have to wait a while to get a listening impression, as the second top plate came from the cutter with some errors, so they are remaking and powder coating a new top panel for me, which I expect to see next week.
I finally got one of these on the bench today and found that I achieved my goal of 75+ watts and made it all the way to 88W! This circuit uses the same topology that I have used in other class A2 amplifiers, which is a pentode front end (807) driving a beefy choke loaded cathode follower (6HS5) that's directly coupled to the output tube (833). I also employed a single damper diode (6KD3) to slow the ramp-up of the high voltage supply, and of course I added a high voltage fuse between the rectifier bridge and the rest of the amp for a little additional safety which is a precaution I don't usually take.
Inside you can see there isn't a whole lot going on in this amp. The SMPS filament supply covers up a lot of the power transformer wiring and some of the high voltage bridge rectifier, as well as a basic 6V DC power supply I added in to heat the 807 (they aren't known for being the quietest tube ever). All the white wire is 15kV rated (and the rest of the smaller PVC jacketed wires are fine up to 1kV), and the single terminals are good for 6kV. The bottom panel holds a very quiet 120mm 12V fan that runs off the 10V filament supply and fires right up through the hole onto the base of the 833, so there's some force air cooling blowing out the top of the glass chimney. I have added a balanced input that can be hooked up to an octal transformer for added flexibility.
I spoke with Monolith about an output transformer when I had this idea and managed to get something made that exceeds my expectations and wasn't overly punishing to my wallet, as their dedicated 833 output transformer is 12K (I needed 5K), amorphous cored (more material required to reach the specified operating level), and a dual C core (possibly leaving a lot of extra space in the can), I asked for an EI core customized unit, and they delivered nicely! While I see 88W at 1kHz/10% THD and 87W at 5% THD, that power only drops to 81W at 10% THD/35Hz, which is above my expectations. The amp is -3dB at 11Hz and shows less than 1dB of drop at 20kHz, which I expected since I had tested one of these previously in a different circuit.
The power transformer and chokes in this amp could be sourced from Hammond, so that wasn't a tough choice, and I went with a nice selection of Mundorf caps and fancy resistors from Parts Connexion where they would work properly. The plate-to-plate feedback resistor in this amp gets a horrendous amount of abuse, and luckily there was a 4.5kV rated Caddock available that worked appropriately.
I will have to wait a while to get a listening impression, as the second top plate came from the cutter with some errors, so they are remaking and powder coating a new top panel for me, which I expect to see next week.
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