Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on August 10, 2025, 09:24:57 pm

Title: 6M5 6EM5 Valves in Push Pull
Post by: TIMBO on August 10, 2025, 09:24:57 pm

Hi Guys,
Got some of the above valves and got a neat little circuit to use them in.
Not a lot of info for PP circuits for these guys.
Plate voltage around 315v
Cathodyne phase inverter
Circuit similar to the "Tweedle Dee"
Any input would be great

Title: Re: 6M5 6EM5 Valves in Push Pull
Post by: uki on August 10, 2025, 10:06:12 pm

Check out the schematic on this post Timbo

https://el34world.com/Forum/index.php?topic=23039.msg252936#msg252936

Title: Re: 6M5 6EM5 Valves in Push Pull
Post by: tubeswell on August 11, 2025, 12:05:10 am

https://frank.pocnet.net/sheets/127/6/6EM5.pdf (https://frank.pocnet.net/sheets/127/6/6EM5.pdf)

Zout = 315/(10/315) = 9,922.5R


Should be able to get away with 8k plate-to-plate load at around 300Vish for PP

Title: Re: 6M5 6EM5 Valves in Push Pull
Post by: AlNewman on August 11, 2025, 12:06:59 am

https://frank.pocnet.net/sheets/084/6/6M5.pdf

https://frank.pocnet.net/sheets/049/6/6EM5.pdf

Kinda looks like a lower output EL84.

Similar to a 6K6, compared to a 6V6.

(Edit:  Tubeswell said basically the same thing as I was typing.)

Title: Re: 6M5 6EM5 Valves in Push Pull
Post by: TIMBO on August 11, 2025, 02:03:48 am

Thanks guys, 8K OT is doable

Title: Re: 6M5 6EM5 Valves in Push Pull
Post by: TIMBO on August 12, 2025, 06:03:17 pm

Thanks guys
(https://i.imgur.com/Nv87Jhi.jpg?2)
I was thinking of having a valve rectifier (EZ81) and series it with a resistor to run it at 12v
Just can find the calculator that will give me the resistor value

Title: Re: 6M5 6EM5 Valves in Push Pull
Post by: tubeswell on August 12, 2025, 06:34:12 pm

Easier way to get power supply sag is with a 10-20w 50R wire wound resistor in series with the FW Bridge and the reservoir cap.

Title: Re: 6M5 6EM5 Valves in Push Pull
Post by: TIMBO on August 12, 2025, 09:45:44 pm

cool

Title: Re: 6M5 6EM5 Valves in Push Pull
Post by: DummyLoad on August 12, 2025, 10:24:44 pm

Seems much like 6AQ5 rated for vertical sweep duty; 9 pin package allows higher B+/G2 V ratings. OT 8K-10K depending on B+/bias method. 


--Pete

Title: Re: 6M5 6EM5 Valves in Push Pull
Post by: TIMBO on August 13, 2025, 02:24:21 am

Hey DL,
40W 100V Line PA EI Core Audio Transformer - Altronics (https://www.altronics.com.au/p/m1130-40w-100v-line-pa-ei-core-transformer/)
These work well for a 8K primary

Title: Re: 6M5 6EM5 Valves in Push Pull
Post by: kagliostro on August 13, 2025, 02:32:47 am

Ciao TIMBO (you have a PM)

Explanation/Documentation on the .pdf file

(https://i.imgur.com/CN05UXP.jpeg)


----


http://diyaudioprojects.com/Technical/Ohms-Law/ (http://diyaudioprojects.com/Technical/Ohms-Law/)

https://sengpielaudio.com/calculator-ohm.htm (https://sengpielaudio.com/calculator-ohm.htm)


Franco


p.s.: read the PM

Title: Re: 6M5 6EM5 Valves in Push Pull
Post by: TIMBO on August 13, 2025, 05:25:09 am

MAN that is mint
Thank you

Title: Re: 6M5 6EM5 Valves in Push Pull
Post by: Merlin on August 13, 2025, 05:30:08 am

With back-to-back transformers you will find the B+ under load is much lower than 315V, maybe around 250V - they naturally sag a lot.
Also the heaters in your schem seem to be missing a connection.

Title: Re: 6M5 6EM5 Valves in Push Pull
Post by: dogburn on August 13, 2025, 11:16:41 am

Looks like a fun project - I'm interested in what it ends up sounding like. Looking at the circuit, I was thinking that if you don't really need two channels, you could mod it to use one 12AX7 triode for a bias-wiggle tremolo like the 6G2 circuit.

Title: Re: 6M5 6EM5 Valves in Push Pull
Post by: TIMBO on August 13, 2025, 04:37:52 pm

Quote from: Merlin on August 13, 2025, 05:30:08 am

With back-to-back transformers you will find the B+ under load is much lower than 315V, maybe around 250V - they naturally sag a lot.
Also the heaters in your schem seem to be missing a connection.

Thanks mate
Just spotted it
The PT's have multiple secondary taps and can be adjusted to increase the overall voltage 

Title: Re: 6M5 6EM5 Valves in Push Pull
Post by: kagliostro on August 13, 2025, 10:55:24 pm

To me the secret Is to use over rated current Transformers, not to overvolt the input of the second Transformer

EDIT: Guessing a bit about the Transformers spec I'll use for T1 a 100VA unit and for T2 an 80VA unit

This will result in a 310V B+ wich will SAG only a bit (or so seems to be to me with my math)

Franco