Okay.. So just playing around with loadlines this morning..
I got wondering if it would be doable to do a semi reasonably priced (relatively) 833A monoblock design..
Looking at the datasheet, it looks like if I were to use a 5K load (Hammond 1642SE), and go for a zero bias, utilizing a mosfet source follower for grid current, it might be within the realm of reality for me.. Just wondering if I've figured this out right..
So here's the loadline I drew:
5K load (2500V / 500mA). biased at 0V, which puts the tube at Va = 1300V / 250mA. This puts plate dissipation at 325W (which is still within the limits of the tube according to the datasheet for ICAS operation).
The grid would need to swing between +50V and -50V.
If I used the 1642SE, it would drop 60V with a 250mA draw, so I would need a 1360V (obviously capable of providing enough current) supply.
I would also need something like +100V & -100V supplies for the mosfet.
Here's the circuit, without many specifics, no power supplies drawn in.
I would need a driver that could easily provide 100Vp-p (very easy obviously. I could build in a good bit of headroom as well)..
Anyways, just wondering if I'm crazy, or if this is a potentially realistic way to build a SET amp with the 833A?
Not sure if I'm calculating power correctly, but I THINK with these operating conditions output power would max out at about 100W RMS..
This is above the power rating of the 1642SE (75W / 300mA), but my current draw is still within spec.. And I don't think there are many OT's within my budget for this type of setup.
This is a bit of a daydream type scenario, but I'm just playing around.
What do you guys think?
I've had Heyboer wind me custom power transformers before, so I would likely go that route again.
I got wondering if it would be doable to do a semi reasonably priced (relatively) 833A monoblock design..
Looking at the datasheet, it looks like if I were to use a 5K load (Hammond 1642SE), and go for a zero bias, utilizing a mosfet source follower for grid current, it might be within the realm of reality for me.. Just wondering if I've figured this out right..
So here's the loadline I drew:
5K load (2500V / 500mA). biased at 0V, which puts the tube at Va = 1300V / 250mA. This puts plate dissipation at 325W (which is still within the limits of the tube according to the datasheet for ICAS operation).
The grid would need to swing between +50V and -50V.
If I used the 1642SE, it would drop 60V with a 250mA draw, so I would need a 1360V (obviously capable of providing enough current) supply.
I would also need something like +100V & -100V supplies for the mosfet.
Here's the circuit, without many specifics, no power supplies drawn in.
I would need a driver that could easily provide 100Vp-p (very easy obviously. I could build in a good bit of headroom as well)..
Anyways, just wondering if I'm crazy, or if this is a potentially realistic way to build a SET amp with the 833A?
Not sure if I'm calculating power correctly, but I THINK with these operating conditions output power would max out at about 100W RMS..
This is above the power rating of the 1642SE (75W / 300mA), but my current draw is still within spec.. And I don't think there are many OT's within my budget for this type of setup.
This is a bit of a daydream type scenario, but I'm just playing around.
What do you guys think?
I've had Heyboer wind me custom power transformers before, so I would likely go that route again.
Last edited:
It does look doable indeed: the amp is easy... problem for me would be the power supply at the 1360v!!
Yea.. Power supply would be a bit of work.. But I think I could still get away with 6CJ3 damper diodes, a big 10uF 2000V Russian surplus cap for the first one, and then 4 of those Solen 51uF 1500V caps after that.. Transcendar could do some 2H / 400mA chokes (He'll do them with 10KV lead wire), and they're hipot tested high enough.
Power transformer could be a custom wind from Heyboer. 1075V - 0 - 1075V, and I guess it would need to be rated for 400mA according to PSUD2.
Last edited:
Why not use a voltage doubler with the lower voltage (higher current) transformer? Unless the PT is potted, the transformer with lower voltage (high current) will yield less mechanical noise than the high voltage transformer for the same rated Power. Cheaper and better quality caps available too.
I too am looking to build a 833 SET.
I too am looking to build a 833 SET.
Yea, I could play around with the power supply design, but I don't think it would be that hard to build a 1360V @ 250mA design in one form or another.
I'm kind of curious if anyone's built an amp with the 833A like this.. Lower voltage, higher current, zero bias.. And a pretty low reflected impedance.. I wonder how it would sound?
Hard to build a HV power supply using a regular FW rectifier? Definitely No! I have 2500-0-2500V potted tranny. It's simple with 866A rectifiers.
But non-potted tranny with such high voltage over 1000V normally have that mechanical hum that I don't like.
Low Voltage, High Current Transformer does not supply DC directly to the tube. The impedance network with CLR components is the impedance of your power supply. If you play with PSUD a bit and uses a CC load, you can find optimal component values for LCLC or CRC or CLR type filters.
I think Meg who builds his SOTA 833A amp had a complaint about PT humming. I am sure though, he runs his 833 at much higher B+ so the PT requirement is rather hefty.
Attached my powersupply for a gu81 amp.
Use a 1000v transformer and you have a great powersupply for a small budget.
Look for transformers and capacitors at radio amateur shops.
Ronny
Use a 1000v transformer and you have a great powersupply for a small budget.
Look for transformers and capacitors at radio amateur shops.
Ronny
Attachments
Last edited:
I used the same scenario but with damper diodes in my GM70
You can easily adjust the final voltage by changing first cap using CLCLC
Its a bit much for that first resistor
I wonder how the damping factor of this amp would be.. I have to imagine it would be pretty low.. I don't quite understand how to calculate that.. And I wonder how much of a factor it would be in the sound of the amp.
5K load is pretty low for this tube. I can't seem to find what the plate resistance of the 833A is. In the datasheet it lists load resistance with 2 tubes in different operating conditions. But nothing regarding class A, and I'm used to seeing a Load resistance and Plate resistance spec, but I don't see Plate resistance listed anywhere.
5K load is pretty low for this tube. I can't seem to find what the plate resistance of the 833A is. In the datasheet it lists load resistance with 2 tubes in different operating conditions. But nothing regarding class A, and I'm used to seeing a Load resistance and Plate resistance spec, but I don't see Plate resistance listed anywhere.
If you have not seen it before, the link may provide some info on the 833A amps.
833A Single End Amp / Pictures | TTRadio
833A Single End Amp / Pictures | TTRadio
Thanks, I haven't seen that thread before..
I'm also now perusing this thread http://www.diyaudio.com/forums/tubes-valves/24424-where-833-amps.html
I'm starting to realize now though, that besides the construction challenges, these tubes don't seem to be very easy to find.. :/
And then, there are quality sockets which are really hard to get. I am making my own from pure copper blocks. I have just only two 833A tube to start.
Chinese 833C and Taylor 833C tubes are cheap and plenty though.
There is also Meg's Midlife Crisis amp thread that will take a couple of days to read.
I do indeed hear a low hum with a 2500V Hammond 733A transformer into a full wave bridge. I had a cover made for it and lined it with Soundcoat sheets and I can't hear it from the listening position, and barely from 3 feet away.
One of these days I'll take the PTs off and have them vacuum impregnated, but I'm in no rush.
One of these days I'll take the PTs off and have them vacuum impregnated, but I'm in no rush.
Same problem with one of my 845 amp. I can't hear it from far away but I can hear it night when standing close to the amp. That's why I only buy old but Potted Ham PT nowadays.
I hope the Vacuum Impregnation helps for you though.
The 833A experiments that I did on an 833A are buried in the Where are the 833A amps thread. Some data and pictures are here:
833 SE | Tubelab
Basically, 1500 volts, 5 K OPT = over 200 Watts RMS at clip!
I asked several times in several posts over the years if anyone ever built a high powered amp using the Hammond 1642SE and never got a valid reply. The 1628SE and 1628SEA both have high frequency resonances that can be in the audio band under the right conditions....like a tube with high Rp (the 833A). I had one custom OPT made, and it had problems over 15KHz.
833 SE | Tubelab
Basically, 1500 volts, 5 K OPT = over 200 Watts RMS at clip!
I asked several times in several posts over the years if anyone ever built a high powered amp using the Hammond 1642SE and never got a valid reply. The 1628SE and 1628SEA both have high frequency resonances that can be in the audio band under the right conditions....like a tube with high Rp (the 833A). I had one custom OPT made, and it had problems over 15KHz.
Last edited:
I had Heyboer wind me a 800 - 0 - 800V z-mount power transformer for my 845 amp, and the mechanical noise is very very low. Much lower than the Hammond 724 I was initially using. And I don't think it was much more expensive.
Wow.. I didn't think it would be putting out that much power.
Anyways, yea I imagine the output transformers would be the real challenge with this amp, even at 5K.
I've read through Magz thread, and it's in a different world to what I'm proposing here.. I think the much lower voltage and 5K impedance I'm going for would make things easier.. But still a challenge..
Where are you finding the Chinese 833C tubes?
I found these
833C - HiFi Triodes, Transmitting Tubes Tubeampdoctor Store
But not exactly cheap..
And then I guess these Taylor 833C's would be the way to go
https://www.rfparts.com/tubes/tubes-trans/tube-tran-taylor/tubes-taylortran-other/833c-tay.html
Or Taylor 833A's
https://www.rfparts.com/tubes/tubes-trans/tube-tran-taylor/tubes-taylortran-other/833a-tay.html
What about these for sockets?
Socket SOC833 to Fit 833A and GU48 etc Valves Tubes Top Caps Available Also | eBay
Last edited:
I found them on eBay. All modern day 833C are all Chinese tubes anyway. But Taylor are probably a better deal and a bit better quality too. I don't know for sure since I haven't bought them yet.
I don't like the Chinese 833 sockets by a long shot. I had considered the ones below. They are a little pricey but I am sure they are better designed for the better grip on the heater pins.
833A GU48 Teflon Socket Pair of Sockets for Power Tube 833A GU48 Valve Vacuum | eBay
Normally, I stay away from all Chinese Plate Caps and sockets. I have the Millen Plate Caps stashed away for this build. The Millen ones also fits for the 866 Plate too. Check on eBay and they come up every now and then.
I spent the past 3 years gathering parts slowly.
Anyway, my amp will use Tango 10K SE OPT for 40W output. Lower B+ and current too. All the Mil Potted Chokes and PT around. All Teflon Caps for B+. Separate B+ circuit on the driver stage. I haven't given much thought of what tube to use for driver yet. I will most likely be using IT with the driver tube. Low B+ Transmitter tube sounds better with IT driver, IMO.
I don't like the Chinese 833 sockets by a long shot. I had considered the ones below. They are a little pricey but I am sure they are better designed for the better grip on the heater pins.
833A GU48 Teflon Socket Pair of Sockets for Power Tube 833A GU48 Valve Vacuum | eBay
Normally, I stay away from all Chinese Plate Caps and sockets. I have the Millen Plate Caps stashed away for this build. The Millen ones also fits for the 866 Plate too. Check on eBay and they come up every now and then.
I spent the past 3 years gathering parts slowly.
Anyway, my amp will use Tango 10K SE OPT for 40W output. Lower B+ and current too. All the Mil Potted Chokes and PT around. All Teflon Caps for B+. Separate B+ circuit on the driver stage. I haven't given much thought of what tube to use for driver yet. I will most likely be using IT with the driver tube. Low B+ Transmitter tube sounds better with IT driver, IMO.
Last edited by a moderator:
I read your thread too and I was able to avoid the mistake with the 1642SE thanks to you!
I do think though, you are running the 833C a bit too HOT? I understand all these are real Power Transmitter and designed to run at red hot plate but would it really sounds good for Audio use with red hot plate?
- Status
- Not open for further replies.