Set 6V6gt Schematic Required

[Digital Man]

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 

[xlr8or]

There are plenty out there if you enter '6V6 single ended circuit diagram' in Mr Google. Here is one to start proceedings:

 

https://diyaudioprojects.com/Schematics/SE-6V6-Amp-Lacewood-Schematic/

[RCAJack]

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.

[Digital Man]

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

[RCAJack]

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.

 

 

[xlr8or]

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 November 20, 2020 by xlr8or

[Digital Man]

Speakers ? That’s the next plan, for another thread

[aussievintage]

 

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.

 

 

[Digital Man]

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.

[Digital Man]

Does anyone know how I can load a short video clip from my email into this thread ?

[RCAJack]

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.

[aussievintage]

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.