driver with gyrator and source follower for GM70

[Tubenstein]

My friend recently sent me a URL regarding driver with gyrator and source follower for GM70.

Is this the best solution to drive the GM70? But lots of feedback to make the gyrator works.

http://www.bartola.co.uk/valves/2018/03/13/gm-70-se-amplifier/

 

[FullRangeMan]

I cant read this schematic but seems a exotic solution. I always read great praise to GM70 drivers as regular tubes, Lampizator use 6N1P/6N6P, DeHavilland use 6AU5GT both with sucess, these tubes are inexpensive.

 

[mogliaa]

Where is the feedback mentioned? Just a classic design with a more linear driver with a hybrid mu-Follower (gyrator load) and well established dc coupled follower to the output valve on fixed bias

Not exotic at all to me

Haven’t built it, just suggested design based on my driver experiences
Ale

 

[mirfak]

Mogliaa,
Could you please, draw a new schematic with a contemporary input tube?
Kind regards, Wojtek

 

[mogliaa]

What do you mean by “contemporary” valve? Schematic won’t change, only bias (e.g. value of cathode resistor) depending on valve used

Thanks
Ale

 

[mirfak]

Something I can buy easily. It is very hard to buy pair of 6sf5gt.

Wojtek

For example:
6C45Pi, 2a3, 6s4s, 2s4s, 6s2s, 6s5s

 

[Wavebourn]

The right way to go.
I use similar solution to drive GK-71

 

[PRR]

...It is very hard to buy pair of 6sf5gt.

6SF5 (6SF5GT, 6F5{G} w/top-cap) is half of a 12AX7 for most practical purpose. (Or rather: 12AX7 is two improved 6F5/6SF5 in one bottle.)

I forget what the Russian "12AX7" is called, but everybody has a hi-Mu triode, usually twin.

What do your guitar-amps use? That will work (with obviously different socket connections).

 

[mogliaa]

Something I can buy easily. It is very hard to buy pair of 6sf5gt.

Wojtek

For example:
6C45Pi, 2a3, 6s4s, 2s4s, 6s2s, 6s5s

Wojtek
I think that If you take the time to search around you will find what you need. There are plenty of examples using the russian valves you mentioned.

If you want western types, you should also consider D3a, 12HL7, amongst other valves which can swing 200Vpp at low distortion.

Have a look here for some examples: http://www.bartola.co.uk/valves/2018/04/01/driving-hard-part-i/#more-7330

Cheers
Ale

 

[mirfak]

Ale,
Thank you! I have just bought 6e6p-dr pairs

 

[45]

Something I can buy easily. It is very hard to buy pair of 6sf5gt.

Wojtek

Not at all. I bought the valve Ale describes , actually 16 RCA's with old logo in mint New-In-Box conditions, here: Electronic Tube and Valve Product Details

The price has gone up a little bit recently but still a bargain! 2x 6SF5 are cheaper than a chinese 12AX7....

Or rather: 12AX7 is two improved 6F5/6SF5 in one bottle

I disagree. The linearity of the 6SF5 is equal or better and it's more consistent. To find a 12AX7 where both triodes are as linear and matched as a matched pair of 6SF5's you need to discard lot of tubes....including some expensive old stuff!

 

[mirfak]

I have bought 6e6p-dr. What is your opinion about "Source follower"? I love tube distortions (sweet, hot sound) and I don't want to lose it. Source follower simplifies the layout but.... you know [emoji6]

 

[Wavebourn]

If you love tube distortions, just add a starving preamp, like 6J1P kit with 12V anode voltage.

 

[mirfak]

I've almost finished 300b preamp . In the near future I would like to build Ale's GM70/6e6p amp. My only doubt is a Source Follower.