GM70 Monoblocks’

[Paul Barker]

My state of mind is much better now I’ve weeded out the failed components and arrived at something that sounds better than the pse 801@ and that Ive put to bed class A2. These GM70’s do such a good job in A1 I see a good amp at the end of the tunnel.

Im glad I bought the Quad’s. Diana is on board as she knows I shall be likely left living on and it’ll help me improving my listening pleasure. The Quads seem much easier to drive than those Australian imports Collin battled with. No disrespect meant to Collin. But these 57’s are light and lively but can thump it out hard with only 6 watts. I dont need a sub and the top end is light and airy, delicate toneful. Position of instruments et allis their forte and Im loving it.

[Paul Barker]

Position of instruments et al is their forte and Im loving it.

Diana is aware of hr situation and her demensia isnt leeding to constant arguments at the phase shes at right now. And I cheish having her in bed every night.

Its the most empty space on earth when shes in ICU…….

Roxy the Staffie will get me through the future phases.

[Nick]

I haven't run the numbers, but I wonder if the el34 in pentode driving the interstage might give you extra gain and a simpler drive for the 6072a, so you might be able to miss the 5687. Also, el84 might do most of the work of a el34 as its only driving the gm70 grid instead of a loudspeaker.

Also another valve I don't see mentioned much is a E130L. I used them to drive a 100tl as a breadboard once with what I thought were good results.

[Ali Tait]

Yes that was a nice amp.

[Paul Barker]

I’ll see if that valve is abailable also like el84. Arguably the best WAD amp.

Ive just stripped out a Rosenblit amp that broke and wasnt made to work on. I didnt like the sound either. I have kept the filament transformer. Not sure about keeping the attenuator. Ive left it for now. Not sure if I can fit everything into this. But could fit a new top panel easily. Got two 1uF silver gold caps if theyre any good I dont buy the bling. Most of it is junk.

I’ll piece the parts and make a new amp with it to drive the GM70. Ought to fit. These Chinese constructed amps are a pain to decommission. Some of the valves cost £50 each today.

[Paul Barker]

The BOTTLE OF BEER WAS A BIRTHDAY PRESENT FROM NAOMI. Lol. I needed it trying to get all that crap out of the chassis. When you take it out there isn’t much of any worth. But the Mcap’s in this instance. Disappointed the stepped attenuator is populated with resistors I dont use. But I guess I cant do everything yet, at least it has a volume control. Think I’ll leave it there. Sowters wouldnt fit anyway. Not sure if everything will fit. Might need more filament voltages, transformer not marked but hoping some are 6v and a few 12v might help. Obviously I’ll have to level the potential on the srpp and the 5687 if used. I’ll still have the srpp for the gain. Though I have a pair of 6072 I cant find them, so Ive ordered a Russian pair.

Those chokes are all .32h 10 ohm. A chocolate fireguard for my needs..

[Paul Barker]

E130L vary in price some are hundreds. I’ll look them up in vade Mecum

[Paul Barker]

Amaising power but the transformers are 50mA.

[Nick]

Ok, so maybe el84 would be a better choice. Just wanted an excuse to mention E130L, I think its a great valve that no one seems to use.

[Paul Barker]

Well theyre popular on ebay. Someone ‘s using them. Not cheap. Must be good. Probably the demand is they may fit in transmitters.

[Paul Barker]

The driver has to swing 240v peak to peak, EL34 more suitable than EL84 especially the EL84 pinches up more trying to achieve the full drive voltage for full power in the GM70. EL34 fits the need. Not possible to get the drive swing without severe distortion.. its not for driving the GM70 to full power.

[Paul Barker]

But I appreciate the suggestions.

GM70 driving GM70 if I had a suitable choke or interstage. But the interstage is OK for EL34 and EL34 is OK in the role.

[Nick]

Why have you drawn a 6k load line for the interstage?
.

[Paul Barker]

That was years ago. I no longer remember what I was working on. I never built it. Shame I didnt take a photo copy of the fresh pages in the Vade Mecum then do my doodles on the copy.

But I see what youre thinking. I usually prefer the sound of interstage without a resistor to load it. As I’m not driving grid current intentionally the load should be close to horizontal, or is it eliptical on a horizontal overall direction?

But I don’t see the required 240v in any angle

On grid current I realise in such a valve as you approach zero bias there will flow an amount of grid current, which may make a distortion.

[Nick]

I was thinking 200v 25ma but I agree more would be better.