833A (GU-48) Amp

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pre65
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#1 833A (GU-48) Amp

Post by pre65 »

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. :wink:
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#2

Post by Prince of Darkness »

You might be interested in this.

http://www.tubelab.com/833SE.htm
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#3

Post by Lee S »

Is he partially naked due to the heat being developed in those valves - or is he just posing for the cam ?? :shock: :lol:
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#4

Post by pre65 »

Lee S wrote:Is he partially naked due to the heat being developed in those valves - or is he just posing for the cam ?? :shock: :lol:
You have my word that I will not pose half naked on the forum. :wink:
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#5

Post by Nick »

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.
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#6

Post by Mike H »

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 :?:

 
 
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#7

Post by James »

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 :-)

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#8

Post by pre65 »

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 ?
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#9

Post by Nick »

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).
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#10

Post by simon »

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.
Fabulous James! First GM70 PP and now 833 (SE presumably?). What else would you like to admit to :).
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#11

Post by simon »

Talking of A2 drivers, I'm thinking about options to drive GM70 in A2. An obvious candidate is 10Y/801A but I don't know too many more suitable valves. Any suggestions?
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#12

Post by Nick »

EL34 would be a option.
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#13

Post by pre65 »

What about something like this ?
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#14

Post by Mike H »

With a step down transformer, interesting.


Not sure about the self stabilising bias part thingy, looks like positive feedback to me.



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#15

Post by Cressy Snr »

Image

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