6V6gt amp build

[Digital Man]

Great, that gives me greater scope for my search, Thanks

[Digital Man]

I spoke with Graham Dicker from Rola today, I can purchase

his Rola OPT 10 SE Output transformer, for not too much money,

does anyone have any thoughts and/or experiences with Rola 

transformers ?

[aussievintage]

14 hours ago, Digital Man said:

I spoke with Graham Dicker from Rola today, I can purchase

his Rola OPT 10 SE Output transformer, for not too much money,

does anyone have any thoughts and/or experiences with Rola 

transformers ?

I used some baby  ones, salvaged from some ancient equipment in a 6005 amp (like a low power 6v6) and they sounded quite good

[VanArn]

15 hours ago, Digital Man said:

I spoke with Graham Dicker from Rola today, I can purchase

his Rola OPT 10 SE Output transformer, for not too much money,

does anyone have any thoughts and/or experiences with Rola 

transformers ?

I take it that Graham Dicker is offering his brand of "Rola'' and not the long gone Rola company that was taken over by Plessey.

[Digital Man]

I have been trying to do that, salvage a pair, but a matching pair is bit thin on the ground, and yes, Graham is offering me a new Rola branded pair, he has also mentioned that in the 1950’s manufacturers were using radio metal instead of audio metal, never heard of this before, so the radio metal only allows you to go down to 50hz and 10khz, this is because of the primary Inductance windings during the 50’s and early 60’s, during the 60’s manufacturers started using GOSS  core allowing smaller transformers to be made with the downside the core started clipping when it saturated while radio metal caused compression, thoughts ?

[aussievintage]

2 hours ago, Digital Man said:

I have been trying to do that, salvage a pair, but a matching pair is bit thin on the ground, and yes, Graham is offering me a new Rola branded pair, he has also mentioned that in the 1950’s manufacturers were using radio metal instead of audio metal, never heard of this before, so the radio metal only allows you to go down to 50hz and 10khz, this is because of the primary Inductance windings during the 50’s and early 60’s, during the 60’s manufacturers started using GOSS  core allowing smaller transformers to be made with the downside the core started clipping when it saturated while radio metal caused compression, thoughts ?

I would have said all transformers clip when the core saturates. The types of speakers used in radios had worse specs than the transformers used, in general. The transformers used in something hifi like an Akai M7/M8 weren't all that large either, but they sounded good.

 

I have at times tweaked frequency response to make a poorer transformer sound better, but there is a limit.

[Digital Man]

Hi, Long shot, but can anyone tell me the make and specs of these transformers ? I couldn’t find anything and the seller doesn’t know either. Thanks 

[VanArn]

With interleaved laminations and only four wires coming from the windings, the main possibility is that the transformers are for the valve heaters.

[Digital Man]

Okay, thanks for the information 

[Digital Man]

What I would like to know is the difference, advantages and disadvantages between these two different styles of output transformers ?

[aussievintage]

20 hours ago, Digital Man said:

Hi, Long shot, but can anyone tell me the make and specs of these transformers ? I couldn’t find anything and the seller doesn’t know either. Thanks 

 

 

The wording talks about amplifiers (plural) using 2 6V6 each, so I would be expecting push pull transformers,  about 15 watt max.  However, as noted, only two wires in - and should be three.  Something strange here.

[aussievintage]

6 hours ago, Digital Man said:

What I would like to know is the difference, advantages and disadvantages between these two different styles of output transformers ?

 

 

They may not be different at all functionally, just one has an end cap and the wiring ends up on one side only, so it can be put on top of a rectangular hole in the  chassis and look neat, with all the wiring underneath.  If you used the others, they would have traditionally been mounted under the chassis , or inside an external case.  You can put a small box over them make them look neat, and run the wirs through neat little holes to the circuit underneath.

[Digital Man]

1 hour ago, aussievintage said:

 

 

The wording talks about amplifiers (plural) using 2 6V6 each, so I would be expecting push pull transformers,  about 15 watt max.  However, as noted, only two wires in - and should be three.  Something strange here.

Hi Aussievintage, Okay, no use for that then. Thanks

[Digital Man]

59 minutes ago, aussievintage said:

 

 

They may not be different at all functionally, just one has an end cap and the wiring ends up on one side only, so it can be put on top of a rectangular hole in the  chassis and look neat, with all the wiring underneath.  If you used the others, they would have traditionally been mounted under the chassis , or inside an external case.  You can put a small box over them make them look neat, and run the wirs through neat little holes to the circuit underneath.

Hi, Okay, as I was thinking if the unenclosed output transformer was maybe of a smaller

type than say the one's with cover's, which may affect performance, especially the bottom

end, but after talking to a winder, that ain't necessarily so, like most things, it all comes

down to construction

[Digital Man]

On 21/11/2020 at 7:08 AM, xlr8or said:

Thanks for sharing @RCAJack. The Cox version without NFB and the triode strapped looks like an excellent design solution to achieve pure SET mode. You're 100% right, the Tech should know how to triode strap the designs shared above to get about 1 watt in power output. The Lacewood design in UL configuration gives about 2 watts in comparison.

 

When looking at the front end input/driver stage my preference in general is to use an octal over a 9-pin mini. Agree on the 5Y3 rectifier in both circuits to provide the DC plate voltage to the 6V6's.

 

@Digital Man what speakers are you planning to run with this flea powered triode set up?

Something small but super efficient, probably a vintage pair of bookshelf

speakers, as this amp is intended for my bedroom, so space won't allow for anything bigger

[Digital Man]

On 20/11/2020 at 5:01 PM, RCAJack said:

Are you dead set on using the 6V6 as your output valve?

 

You're probably aware it's not actually a triode (SET stands for 'single ended triode) but it can be hooked up in triode mode. Anyway, it doesn't seem to be the most common tube in single ended hi-fi amps (although it's mega popular in single ended guitar amps of course). The cool looking build that @xlr8or has linked is not actually triode connected, for what it's worth.

 

Assuming you've got some output transformers with around a 5K primary,  you could consider some alternative valves and get a bit more power, plus the opportunity to try out more circuits. It really depends on your priority.

 

It'd help to know the exact specs of your parts to suggest more options if that's of any interest.

Okay, the power transformer that I will be using, the specs are

Heater Voltage is 6.3 VAC

HT for valve rectifier is 400 volts

Has a 5 volt AC tap as well for the rectifier heater

physical capacity is 60 VA ( Could possibly be more )

So, what other tubes do you think that I could use in

SE or SET mode besides the 6V6GT ?

[Digital Man]

On 20/11/2020 at 10:59 PM, RCAJack said:

I've found a detailed article on doing a triode connected 6V6 amp by Jason Cox of boozhoundlabs (currently offline so the link goes to archive.org). Depending on the exact voltage coming off your power transformer, your tech may need to tweak things a little but this seems to be a pretty basic example of what you're looking for. I think it'll give you output in the 1-2W range. Jason used the Hammond 125ESE output transformers which are about $100 each plus shipping from mouser.

 

Jason Cox explains this is his modded version of a circuit from diyaudio.co.kr (below). The Jason Cox version omits the negative feedback and connects the output valve in triode mode. There should be a heap of similar circuits you could modify to triode mode in a similar way. Maybe talk to your tech about making the triode mode switchable as you should get a tiny bit more power with the valve connected as a tetrode.

 

 

I am considering your suggestion about going SET rather than SE

[aussievintage]

1 hour ago, Digital Man said:

So, what other tubes do you think that I could use in

SE or SET mode besides the 6V6GT ?

 

In the same family, and pin compatible 6L6, 6550, and quite a few others.  Then there's the 6AQ5, EL34 and EL84.. Many more, including some more obscure choices.  You really can make any power valve work.  How about a 6CM5, or 6DQ6.  Or triode/pentode combos like 6GW8, 6BM8.  Many many possibilities.

 

Of course there's the real directly heated triodes, like 45, 2A3, 300B

[Digital Man]

9 minutes ago, aussievintage said:

 

In the same family, and pin compatible 6L6, 6550, and quite a few others.  Then there's the 6AQ5, EL34 and EL84.. Many more, including some more obscure choices.  You really can make any power valve work.  How about a 6CM5, or 6DQ6.  Or triode/pentode combos like 6GW8, 6BM8.  Many many possibilities.

 

Of course there's the real directly heated triodes, like 45, 2A3, 300B

Yes, but will they work well with my power transformer ?

I gave the specs above

[aussievintage]

11 hours ago, Digital Man said:

Yes, but will they work well with my power transformer ?

I gave the specs above

 

 

Unfortunately 400V will give you too much for even the 6V6 you have been talking about without some means of reducing the HT.    The EL34 can handle the voltage, if your transformer can handle the extra heater current.

 

You're going to have to start looking at the data sheets.  Here's a good resource.  https://tdsl.duncanamps.com/tubesearch.php

Edited July 4 by aussievintage

[Digital Man]

7 hours ago, aussievintage said:

 

 

Unfortunately 400V will give you too much for even the 6V6 you have been talking about without some means of reducing the HT.    The EL34 can handle the voltage, if your transformer can handle the extra heater current.

 

You're going to have to start looking at the data sheets.  Here's a good resource.  https://tdsl.duncanamps.com/tubesearch.php

 

7 hours ago, aussievintage said:

 

 

Unfortunately 400V will give you too much for even the 6V6 you have been talking about without some means of reducing the HT.    The EL34 can handle the voltage, if your transformer can handle the extra heater current.

 

You're going to have to start looking at the data sheets.  Here's a good resource.  https://tdsl.duncanamps.com/tubesearch.php

Well, that power amp came out of a radiogram that was feeding 6v6gt as se

[aussievintage]

7 minutes ago, Digital Man said:

 

Well, that power amp came out of a radiogram that was feeding 6v6gt as se

 

Well ...

 

 

See the VaMax of only 350VDC?   400 ac, rectifies (full wave) to about 1.4 times - 560 volts DC.

 

Maybe you mean it's a 200 volt a side centre tapped HT winding?  That'll give  under 280 volts HT (less of course after losses) say, about 250V which is good

 

 

 

[Digital Man]

1 hour ago, aussievintage said:

 

Well ...

 

 

See the VaMax of only 350VDC?   400 ac, rectifies (full wave) to about 1.4 times - 560 volts DC.

 

Maybe you mean it's a 200 volt a side centre tapped HT winding?  That'll give  under 280 volts HT (less of course after losses) say, about 250V which is good

 

 

 

Well, they were the figures given to my by Earle, based on the transformers dimensions and weight, problem with it is, there are no markings on it whatsoever, I might have to send it in to have everything verified 

[Digital Man]

Just now, Digital Man said:

Well, they were the figures given to my by Earle, based on the transformers dimensions and weight, problem with it is, there are no markings on it whatsoever, I might have to send it in to have everything verified 

Having said that, trust me, you wouldn’t want to drop that sucker on your foot, even with safety boots on 

[VanArn]

Yes, get your technician to test the mains transformer to find out what voltage is present on the HT windings. Was the HMV radiogram an earlier mono type as 6V6GT valve suggests such a scenario.