833A (GU-48) Amp
- pre65
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#1 833A (GU-48) Amp
Don't know why, but I keep having "thoughts" about using these monsters in a single ended amp.
I know Darren had one, and at Owston Nick admitted a fancy for them as well.
My question is, what is likely to be the minimum HT to get them working well in an audio amp and what spec of output transformer would likely be required.
I'm hoping that something like 1 - 1.5KV would be enough.
This is (to me) the ultimate "once in a lifetime" amp.
I know Darren had one, and at Owston Nick admitted a fancy for them as well.
My question is, what is likely to be the minimum HT to get them working well in an audio amp and what spec of output transformer would likely be required.
I'm hoping that something like 1 - 1.5KV would be enough.
This is (to me) the ultimate "once in a lifetime" amp.
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
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#2
"We need to grab the Bull by the scruff of the horns!"
Prince.
Prince.
- pre65
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#4
You have my word that I will not pose half naked on the forum.Lee S wrote:Is he partially naked due to the heat being developed in those valves - or is he just posing for the cam ??
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
#5
Ye, as you say, the 100th has prompted a certain desire towards the 833. I think something like 1500v @ 150ma, grid at -20v, with a direct coupled A2 driver and a 7k5 transformer could be expected to produce something in the order of 75W.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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#6
His chest needs a serious shaving.
(Not Nick's I don't mean)
A simple way of getting 1,500V might be stacking 3 x 500V supplies on top of each other
(Not Nick's I don't mean)
A simple way of getting 1,500V might be stacking 3 x 500V supplies on top of each other
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
#7
I have to admit to having a pair of 833's, a pair of hammond 1642SE's and four 5v 10 amp smps waiting in the wings to keep me quiet when the gm70's are finished. I plan to use the 1.1Kv 250ma PSU's i have bult for the GM70 PP amp.
The big question is how to drive them, I must admit Tube lab's powerdrive looks good. Phillip at bluebell hinted he is working on some 4:1 SE interstages with hammond for a KT88 or 300b driver but i have not been able to get any more than that from him than that.
I will be interested to see how you guys get on
Best Regards
James.
The big question is how to drive them, I must admit Tube lab's powerdrive looks good. Phillip at bluebell hinted he is working on some 4:1 SE interstages with hammond for a KT88 or 300b driver but i have not been able to get any more than that from him than that.
I will be interested to see how you guys get on
Best Regards
James.
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#8
I think (from memory) that Darren used an existing low powered SE amp to drive his 833a. But I don't know if it was in A2.
Is there any point in going for normal class A with an HT of around 1.2KV and using an existing amp as the driver ?
Is there any point in going for normal class A with an HT of around 1.2KV and using an existing amp as the driver ?
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
#9
It will make some sound, not that much, but then again you probably dont need that much.
James, my musing was thinking about using the same sort of driver as I did for the 100Th, if anything the 833 would be a easier load, less grid current as the 100Th was sitting with the grid at +20, the 833 would be about -20v. Its similar to the power drive, just using high gm beam pentodes with a active load (another pentode).
James, my musing was thinking about using the same sort of driver as I did for the 100Th, if anything the 833 would be a easier load, less grid current as the 100Th was sitting with the grid at +20, the 833 would be about -20v. Its similar to the power drive, just using high gm beam pentodes with a active load (another pentode).
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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#10
Fabulous James! First GM70 PP and now 833 (SE presumably?). What else would you like to admit to .James wrote:I have to admit to having a pair of 833's, a pair of hammond 1642SE's and four 5v 10 amp smps waiting in the wings to keep me quiet when the gm70's are finished. I plan to use the 1.1Kv 250ma PSU's i have bult for the GM70 PP amp.
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#13
What about something like this ?
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The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
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#14
With a step down transformer, interesting.
Not sure about the self stabilising bias part thingy, looks like positive feedback to me.
–
Not sure about the self stabilising bias part thingy, looks like positive feedback to me.
–
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
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#15
You're maaaad the lot of you!
Maaaad I say!