GM70 SET

What people are working on at the moment
User avatar
Ali Tait
Eternally single
Posts: 4374
Joined: Fri Jun 08, 2007 8:10 pm
Location: Galashiels

#286 Re: GM70 SET

Post by Ali Tait »

Try another card Paul?
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8867
Joined: Mon May 21, 2007 9:42 pm

#287 Re: GM70 SET

Post by Paul Barker »

I thought that but it's linked to my business bank account as I am a business user. I purchased a work related item over the weekend and it worked fine. It seems to be a problem with the seller. As it is a weekend no response from seller as of yet.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8867
Joined: Mon May 21, 2007 9:42 pm

#288 Re: GM70 SET

Post by Paul Barker »

It turns out Russian Government won't allow PayPal purchases by businesses outside Russia. That is to say a Russian Business cannot sell to a UK Business.

So the seller has sent me a payment request via a USA organisation which is set up to solve this problem.

I have paid their invoice. So I may get some valves or I may have been scammed. But as he has 100% feedback, probably OK.

Putin I suppose.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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.

#289 Re: GM70 SET

Post by Dave the bass »

Paul Barker wrote:
Putin I suppose.
Yeah, thats the best way I reckon.

He has a box, he has some valves, he has a fella on the other side of the world that wants them and has paid for them in advance. So...

Putin box and send them to him...

Ha! SWIDT?
"The fat bourgeois and his doppelganger"
User avatar
andrew Ivimey
Social Sevices have been notified
Posts: 8307
Joined: Mon Jun 11, 2007 8:33 am
Location: Bedford

#290 Re: GM70 SET

Post by andrew Ivimey »

Witty,very witty!
Philosophers have only interpreted the world - the point, however, is to change it. No it isn't ... maybe we should leave it alone for a while.
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.

#291 Re: GM70 SET

Post by Dave the bass »

andrew Ivimey wrote:Witty,very witty!
It was one of .....

Ha!
"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

#292 Re: GM70 SET

Post by simon »

It's about time I got this boxed up, and I think monoblocks is the way to go for various reasons.

I reckon I have pretty much most bits I need for 2 amps, though I might need some more trafos. I'm sold on separate HT supplies for the 12GN7 driver so I need a couple of 25VA mains transformers. But I'm wondering whether I can get away without a 6.3V trafo by sharing an existing winding for the 12GN7 and 2 6AX4 damper diode heaters...

Now ordinarily I wouldn't even consider having the signal and rectifier valves on the same winding, but I have a couple of Tentlab heater supplies which at <1A can supply 6.3V DC out for 6.3V AC in.

http://www.tentlabs.com/Products/Tubeam ... index.html

The question is how likely is the regulator to shield the 12GN7 from the 6AX4 switching spikes etc.? As far as I can see it's "just" a low drop chip regulator so would probably do an adequate job, but not as good as galvanic isolation.

Thoughts?

I think I'm inclined to get a couple of Hammond 266JB6 (6.3V 1.2A) from Philip Ramsey for the 12GN7s and run the dampers of the mains tx. They're £12 each inc. vat, how the 0.3A versions are £31 each I don't know.
User avatar
ed
retired
Posts: 5384
Joined: Thu Jun 21, 2007 4:01 pm
Location: yorkshire
Contact:

#293 Re: GM70 SET

Post by ed »

Hi Simon

I've got a 266 PA6 sitting on the shelf which just failed to sell on ebay...it may be ott for your requirement though:

6.3v @ 6a or 12.6 @ 3a

also a couple of Coleman heavy duty regs with big heatsinks I was using them for 6.3v @ 4 amps....
Last edited by ed on Thu Apr 26, 2018 12:25 pm, edited 1 time in total.
There's nowhere you can be that isn't where you're meant to be
Ant
Shed dweller
Posts: 2332
Joined: Mon Jul 31, 2017 6:45 pm
Location: Yorkshire

#294 Re: GM70 SET

Post by Ant »

I reckon pulses would still get past the reg board, id just get hold of some tx's. A couple of 6v toroids would do the job fine for the diodes
Edit: wot ed said
Also starring Rex Hamilton as Abraham Lincoln

www.bte-designs.weebly.com
User avatar
pre65
Amstrad Tower of Power
Posts: 21373
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex/Suffolk border.

#295 Re: GM70 SET

Post by pre65 »

I use a 9v 10va frame transformer, then 2 X 1R then a DIY Hi-fi ultra low noise module for the 12GN7 on my GK71 amp.

The 1R just drop the volts enough to stop the module heatsink getting too hot.
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)
simon
Thermionic Monk Status
Posts: 5600
Joined: Thu May 24, 2007 11:22 am
Location: People's Republic of South Yorkshire

#296 Re: GM70 SET

Post by simon »

Thanks ed, but I need 2, one for each mono.

I should probably have been a bit clearer - if I have separate trafos I'll most likely just run the 12GN7s on AC, they work fine like this. The Tentlabs are just a thought to enable me to potentially use the same winding.
User avatar
pre65
Amstrad Tower of Power
Posts: 21373
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex/Suffolk border.

#297 Re: GM70 SET

Post by pre65 »

If I were doing another one I'd probably use some LT1083 modules off Ebay for under a tenner each.

Like this

https://www.ebay.co.uk/itm/LT1083CP-Lin ... 1438.l2649
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)
simon
Thermionic Monk Status
Posts: 5600
Joined: Thu May 24, 2007 11:22 am
Location: People's Republic of South Yorkshire

#298 Re: GM70 SET

Post by simon »

Sigh. Nearly another year has passed and I'm no further forward, surely this year won't be as horrid as last...

Of course, the problem with DIY is nothing's ever "finished" and I'm now considering a slightly different tack which I would appreciate the panel's views on.

The Quasars are no more (sorry James) - I'm using the GM70 amp directly coupled to the FE208Esigmas from 150Hz up on a plain baffle, and a couple of cheap 3116 class D subwoofer amps (with built in 180Hz low pass filters) directly coupled to the 285GMFs in H frames. Removing the series crossovers was an obvious improvement when I first tried it in the Quasars, even with £25 of Chinese class D amp and a SMPS PS.

To control 2 amps needs some kind of pre/control amp to split the signal and balance the volume from each driver. I'm a little reluctant to add another stage, like a 26 say, as I don't need any more gain. So I wonder about putting the 12GN7 in the pre and leave just the GM70 outputs in the power amp. I think I'll end up with a valve amp driving the 285GMFs too, so what are the pros and cons of sharing the driver valve and then splitting the signal to two separate amps?

I can't ever remember seeing this type of arrangement so I'm a little sceptical of how well this might work. I think I'd need something like a White cathode follower after the driver to drive the cables to the output valves, but what are people's thoughts?
Attachments
Driver split output.jpg
User avatar
ed
retired
Posts: 5384
Joined: Thu Jun 21, 2007 4:01 pm
Location: yorkshire
Contact:

#299 Re: GM70 SET

Post by ed »

slightly OT with respect to GM70 but:

I'm watching with interest Simon...do it, do it....

It's not a million miles from the thing I was working on when I had a bit of a rest in 2014. It was prompted by the failure of the AMT OB. I never picked it up again later...maybe I should.

those TPA3116 are awesome in my opinion and I still use one to drive the electrostatics.
ob class d.jpg
there is a volcontrol/attenuator in each tpa3116 which would be adjusted to balance the two drivers(using clio to save the risk of madness)
There's nowhere you can be that isn't where you're meant to be
User avatar
Nick
Site Admin
Posts: 15707
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#300 Re: GM70 SET

Post by Nick »

I did something similar with my first 211. 76 + 45 driver stage in one box, coax to the 211 grid. Should be fine. I would think that unless you are going via Manchester the extra capacitance of the coax would not be a problem for the pentode driver.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Post Reply