GM70 SET

What people are working on at the moment
Post Reply
simon
Thermionic Monk Status
Posts: 5600
Joined: Thu May 24, 2007 11:22 am
Location: People's Republic of South Yorkshire

#1 GM70 SET

Post by simon »

I've played with 6EM7, 45, 2A3 and 300B and I'm toying with something a little larger, maybe a 211 or GM70. I have neither valves, nor means to heat them, nor big mains txs. I do have some 100mA 25W 5k opts, and some 1uF 1000V Mundorf silver coupling caps.

So after a suggestion from Andrew a few days ago about GM70 I've been having a bit of a think. Now the thought of heading towards 1000V is rather scary and I have a strong sense of my own mortality so whilst it might seem a bit arbitrary I think any plans will be with under 1000V (geez, what am I saying!).

The largest mains txs I have would give me about 450V as an OP after voltage drops and cathode bias - 5k opts @ 450V 60mA would give ~4.2W. But I'm using the mains txs anyway.

Heading up to 800V 100mA would give ~15.6W; 900V 100mA gives ~21.6W. Rock and roll!

I guess 20V 3A filaments will have to be DC - not sure of any regs that might make a simple current reg though.

I haven't looked too far at drivers. For 21W I'd need over 160V swing. I guess a 10Y would be interesting, though I'm a bit weary of DHT driver filaments. Or perhaps a 6N6P? Or a 6N2P/6N6P Aikido? I'm not particularly convinced about the small Russian valves I have though.

But I wonder if 6EM7/6DN7 might be an interestng choice?

So what do peeps think so far? Or do I need a good talking to?
User avatar
pre65
Amstrad Tower of Power
Posts: 21373
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex/Suffolk border.

#2

Post by pre65 »

Go for it !!

My humble effort runs at 600V HT.
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
User avatar
Nick
Site Admin
Posts: 15707
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#3

Post by Nick »

My first attempt was driven by a 6em7 did ok. Heating is a problem, I found with a bit of care and some big heatsinks its possible to use three terminal regs as current regs to heat them. I have most of the bits on a heatsink somewhere, you are welcom to borrow them to aid the project.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Andrew
Eternally single
Posts: 4206
Joined: Thu May 24, 2007 2:18 pm

#4

Post by Andrew »

Hi Simon,

6EM7 would be good, I always thought it might make a good 300B driver, so why not a GM70.

Go for it....

-- Andrew
simon
Thermionic Monk Status
Posts: 5600
Joined: Thu May 24, 2007 11:22 am
Location: People's Republic of South Yorkshire

#5

Post by simon »

Thanks for the encouragement chaps :).

6EM7 has the appeal on 6.3VAC - nice and easy and compact. Only ok Nick?

Thanks for the offer of the filment stuff Nick. Did you use something like LM338?

If I'm looking at, say, 1000V does anybody know what AE chokes are rated at? I guess I could put them in the earth rail to be sure.
Andrew
Eternally single
Posts: 4206
Joined: Thu May 24, 2007 2:18 pm

#6

Post by Andrew »

I think the problem with 6EM7 is the linearity of the first stage, I always thought it could be loaded by a CCS, might even have one around, for that job, somewhere.

-- Andrew
User avatar
Dave the bass
Amstrad Tower of Power
Posts: 12273
Joined: Tue May 22, 2007 4:36 pm
Location: NW Kent, Darn Sarf innit.

#7

Post by Dave the bass »

Your audience awaits! Get building :lol:

DTB
"The fat bourgeois and his doppelganger"
simon
Thermionic Monk Status
Posts: 5600
Joined: Thu May 24, 2007 11:22 am
Location: People's Republic of South Yorkshire

#8

Post by simon »

Andrew wrote:I think the problem with 6EM7 is the linearity of the first stage, I always thought it could be loaded by a CCS, might even have one around, for that job, somewhere.
Ah right, I'll bear that in mind when I look at the curves. I have some 6DN7s too which I've never used - I'll check those out too.
simon
Thermionic Monk Status
Posts: 5600
Joined: Thu May 24, 2007 11:22 am
Location: People's Republic of South Yorkshire

#9

Post by simon »

Dave the bass wrote:Your audience awaits! Get building :lol:
I wouldn't hold your breath Dave - it's gonna be a bit of a long term job this one. Well, until my curiosity gets the better of me any way :wink:
User avatar
pre65
Amstrad Tower of Power
Posts: 21373
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex/Suffolk border.

#10

Post by pre65 »

The 12GN7 I was using on my GM70 are now resting in the spares box so if you want to try them PM me your address.
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#11

Post by Mike H »

Dave the bass wrote:Your audience awaits! Get building :lol:

DTB
With bated breath, even :)

.
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
simon
Thermionic Monk Status
Posts: 5600
Joined: Thu May 24, 2007 11:22 am
Location: People's Republic of South Yorkshire

#12

Post by simon »

pre65 wrote:The 12GN7 I was using on my GM70 are now resting in the spares box so if you want to try them PM me your address.
Thanks Phil, I'll bear that in mind :).
User avatar
Nick
Site Admin
Posts: 15707
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#13

Post by Nick »

6EM7 has the appeal on 6.3VAC - nice and easy and compact. Only ok Nick?
If I remember, it was a very nice ok, not a ok ok. Didnt have very good transformers then so I never heard what if could do. But it was good enough to make me want to build the first 211.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
simon
Thermionic Monk Status
Posts: 5600
Joined: Thu May 24, 2007 11:22 am
Location: People's Republic of South Yorkshire

#14

Post by simon »

6EM7 sounds like a decent place to start then.
User avatar
Dave the bass
Amstrad Tower of Power
Posts: 12273
Joined: Tue May 22, 2007 4:36 pm
Location: NW Kent, Darn Sarf innit.

#15

Post by Dave the bass »

simon wrote:6EM7 sounds like a decent place to start then.
...y'mean its not finished yet?

Northern slacker!

:D

DTB
"The fat bourgeois and his doppelganger"
Post Reply