• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

813 and gm70

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Koifarm

Koifarm

Banned
Joined 2005
Looks good and not that difficult to build.

This one i use(see photo) with modified driver( now 6n6p).
 

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Koifarm

Koifarm

Banned
Joined 2005
I shall tomorrow look for the schematic.

The transformers came with the chinese amp. This amp was cheaper complete then building yourself. About €400,-. Just did some modifications.

Current building a GU81m amp wih the FU13 as driver.
 

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L

lexx21

Member
Joined 2011
Actually what kind of OPTs is a good question for 813. Who makes an OPT that will sound good as well as not break the budget. I have a set of 813 tubes that I picked up a couple of years ago but haven't built anything with them due to the cost (high cost) of the OPT.
 
M

Matt BH

Member
Joined 2009
Hi M Gregg, I think 6e5p with Rods shunt cascode takes some beating driving GM70. Ale has a good write up of the topology here:

The Shunt Cascode Driver | Bartola Valves

There is also a lengthy thread here about it somewhere.

I use a pair of 6K to 8R output trannys. They were a bargain unknown from eBay that seem to be custom Audio Note jobs. Measure very well and are heavy as @#$%. HT is 1KV.

Don't have a schematic at the mo as it's still on the breadboard. I can scribble down what it is now if you need but it ain't pretty:p

Cheers
Matt.
 
M Gregg

M Gregg

Disabled Account
Joined 2010
Matt BH said:
Hi M Gregg, I think 6e5p with Rods shunt cascode takes some beating driving GM70. Ale has a good write up of the topology here:

The Shunt Cascode Driver | Bartola Valves

There is also a lengthy thread here about it somewhere.

I use a pair of 6K to 8R output trannys. They were a bargain unknown from eBay that seem to be custom Audio Note jobs. Measure very well and are heavy as @#$%. HT is 1KV.

Don't have a schematic at the mo as it's still on the breadboard. I can scribble down what it is now if you need but it ain't pretty:p

Cheers
Matt.
Click to expand...

Yes the output Tx's are an issue.
But if SY is correct they ain't gotta be silver..LOL

NB nice to hear from you matt..:D

But can you beat an Ongaku..

But what about the 807 as a driver?

Regards
M. Gregg
 
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M

Matt BH

Member
Joined 2009
Good to hear from you too:D

Certainly don't need silver in your transformers or anything at audio frequencies imo. Lol.

Not sure about beating an Ongaku, never heard one. I'm sure my speakers and ears are not good enough:(

I thought about 5B255M (807) to drive mine as they look very nice next to a GM70. In triode I'm sure they would be fine but you would need either 3 stages or a rather high output pre amp. I prefer two stages and just a volume control if I can get away with it without too many compromises.

Of course it would also be possible to use Rods circuit and another DHT. That would be excellent.

As you can see I don't mind some sand in the signal path. YMMV

Cheers
Matt.
 
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