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6V6gt amp build


Digital Man

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Hi All, Can someone help and/or provide me with a SET 6V6gt schematic ? I don’t understand schematics and my local tech guy, who is going to build it for me using vintage iron and parts, wants me to send him said schematic. Thanks 

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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.

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I salvaged everything from a HMV radiogram, circa 1959, it came as a single ended 6V6gt, I had half of it made into a Fender Champ clone guitar amp, using the Goodman speaker that came from the radiogram as well, I still have the chassis, half the tubes, the power transformer with the huge choke to make the beginnings of the 6V6gt set amp, stereo, class A

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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.

6v6hifi.gif.543beb56e1ea6b71af00540829e56a70.gif

 

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.

 

image.png.4bc697b30f02974b7b3e452398c1df91.png

 

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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?

Edited by xlr8or
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Having built many different SE and SET amps from leftover parts from old equipment like this,  let me just say you can achieve a very fine sounding amp.   The 6V6 can sound great in triode mode, and I am sure you could get a couple of watts from it, depending on voltage and loading etc.   That makes it roughly on the same level as the 2A3 DHT style amps many people like, and that I am currently using.  My speakers are 95db efficient and I get told to turn it down :) 

 

Also, with a 6V6 octal socket, you can also plug in 6L6, 6550, and all sorts of valves in that family.  They will run at 6V6 bias conditions aprox. but will sound subtly different, and allow you to experiment.

 

 

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I have been wanting to hear a se, set amp for a while, this will whet my appetite, I am sure, you are right about what you can achieve by scavenging such parts, trust me though, what I scored was not the typical punny iron, this power transformer can definitely break your foot if you dropped it thus, as an aside, the Fender Champ clone that I had built from half of the parts, using a 6V6gt sounds great, more than enough volume for what I need it for, now to finish off the parts leftover into a set amp.

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3 hours ago, aussievintage said:

Also, with a 6V6 octal socket, you can also plug in 6L6, 6550, and all sorts of valves in that family.

 
Noting that the 6V6 uses a modest .45A of filament current whereas a 6550 uses more like 1.6A. OP should figure out the total current draw from all the 6.3V heaters in the radiogram to get an idea of how much current it’s intended to deliver.

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8 hours ago, RCAJack said:

 
Noting that the 6V6 uses a modest .45A of filament current whereas a 6550 uses more like 1.6A. OP should figure out the total current draw from all the 6.3V heaters in the radiogram to get an idea of how much current it’s intended to deliver.

 

For sure.   I only meant the socket wiring is compatible.  Heater current, and indeed bias current (if you want to run those bigger valves at their best), will put a strain on a transformer and rectifier etc that was meant to only power 6V6 valves.

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  • 3 years later...

Hi All, Hope everyone is well, it has been a while, 4 years to be exact, I am still chasing vintage output transformers for this build,

my tech has asked me to get the se output transformers with these specs,

15 Watts

Multi tap output - 8-4 Ohms

Input primary impedance - 7k

Does these seem okay ? or is he aiming a bit high ?

The Power transformer that I am using, has no brand or anything on it, it is the one that I salvaged from the said radiogram,

I did measure and weigh it and gave those details to Earle, he says that from those figures it has

Heater Voltage - 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 )

Based on this information, which SE output transformer ratings should I be seeking for this SE 6V6GT build ?

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5 minutes ago, Digital Man said:

Hi All, Hope everyone is well, it has been a while, 4 years to be exact, I am still chasing vintage output transformers for this build,

my tech has asked me to get the se output transformers with these specs,

15 Watts

Multi tap output - 8-4 Ohms

Input primary impedance - 7k

Does these seem okay ? or is he aiming a bit high ?

The Power transformer that I am using, has no brand or anything on it, it is the one that I salvaged from the said radiogram,

I did measure and weigh it and gave those details to Earle, he says that from those figures it has

Heater Voltage - 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 )

Based on this information, which SE output transformer ratings should I be seeking for this SE 6V6GT build ?

 

You can't get more than about 5 watts (less in triode mode) out of a SE 6V6, so the transformer is way oversized.

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5 minutes ago, Digital Man said:

Hi, Do you mean the output transformer ?

 

The power requirement of 15 watts will demand an oversized OT. Might be worth looking for something around 10 watts maximum. Nothing wrong with the 7K primary impedance. Tango FE-12S would be nice. They're recommended for 6V6 SET design use for 8 and 16 ohm output.

 

images-3.jpeg.0e71b334e9e33e33a0d7cbab243a113d.jpeg

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Well, that wasn't my recommendation, it was the recommendation of the

audio engineer who is going to build it for me, but I did have my suspicion's,

that is why I am asking for verification for the specs on the output transformers

 

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28 minutes ago, xlr8or said:

 

The power requirement of 15 watts will demand an oversized OT. Might be worth looking for something around 10 watts maximum. Nothing wrong with the 7K primary impedance. Tango FE-12S would be nice. They're recommended for 6V6 SET design use for 8 and 16 ohm output.

 

images-3.jpeg.0e71b334e9e33e33a0d7cbab243a113d.jpeg

I would have thought 10 watts would be the way forward, rather than 15 watts

Could the primary go any lower than 7k ? or just leave it at 7k ?

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10 minutes ago, Digital Man said:

I would have thought 10 watts would be the way forward, rather than 15 watts

Could the primary go any lower than 7k ? or just leave it at 7k ?

 

You can go lower down to 5k. Power output will be 1w less. Have a look at the load resistance values below. I'd aim for cathode biased close to 5.5w.

 

Screenshot_20240630_192153_Drive.thumb.jpg.c44da8f09c7acaf5b89530df06325d11.jpg

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Okay, in se mode, power max would be 5 watts, yes ? so if 10 watts is still overkill,

then I could go down to 5 watts and no lower ? and how low could I go with the primary ?

5K ? or even a bit lower ?

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6 minutes ago, Digital Man said:

Okay, in se mode, power max would be 5 watts, yes ? so if 10 watts is still overkill,

then I could go down to 5 watts and no lower ? and how low could I go with the primary ?

5K ? or even a bit lower ?

 

Did you note the distortion figures for those power levels?  8 and 12%   You are never going to listen at those levels, so yes, 5 watts is plenty.

 

Want a sweet sound, get 5k primary and strap the 6V6's for triode mode.

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I really appreciate your help here, I wonder why he recommended

those other specs originally ? So, just to confirm, I should be looking

out for a output transformer with a primary impedance of 5k,

multi tap output 4-8 Ohms and 5 Watts, yes ?

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40 minutes ago, Digital Man said:

I really appreciate your help here, I wonder why he recommended

those other specs originally ? So, just to confirm, I should be looking

out for a output transformer with a primary impedance of 5k,

multi tap output 4-8 Ohms and 5 Watts, yes ?

 That's where I would start.   5k to 7k all OK

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