GM70

What people are working on at the moment
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8247
Joined: Mon May 21, 2007 9:42 pm

#1 GM70

Post by Paul Barker »

Well anyway, while wandering about triode connected tomfoolery which only diy community seem obsessed with.

Press on with true triodes.

So I’ve found yet another transformer from my stash. 1185-o-1185 @360mA if used choke input.

Image

Image

Image

best free image hosting

Also pictured are the ideal mono lock power transformers for the eventual ultimate mono lock gm70 which only lacks suitable matched chokes.

Then pictured is the superb choke presently in use.

So with newly found long forgotten ht transformer, choke presently in use. Brand new amp with tributes opts on designed for 212 but gm70 vertually a 212 much more than it’s an 845 which it’s laughingly compared to by some.

Could build it monoblock signal stages. Combined power until I’ve procured matching ginormous chokes! Permission to spend that kind of sum presently withheld!
"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: 8247
Joined: Mon May 21, 2007 9:42 pm

#2 Re: GM70

Post by Paul Barker »

oh : duty cycle 5 min on 10 min off.

As useful as a one legged man in an arse kicking contest in a class A valve amp. Bugger!

well, maybe if i only use it for gm70@100mA each and use another power supply for VA and driver.

but looks better to use the pair of transformers with the one big choke all in one supply until more big chokes come on board in my hoarders paradise. Starting with 1460v better than starting at 1185v to boot! opens up more operating points and more smoothing options
"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: 8247
Joined: Mon May 21, 2007 9:42 pm

#3 Re: GM70

Post by Paul Barker »

Found another maybe suitable power transformer which I’ve yet to test. I’ll put a 572b adjustable load on it and see % drop compared to unloaded. Should be 10% at rated current.

More GM70s than I remembered, and 1 gk71, but only one GM70 was Copper Plate. Somewhere there is another. However the two coppers I just bought have a backup one.

Heat sinks should do a Mofo when I get around ….

That power output stage is done, Nick and I had it at Owston. Simple’s life I could just convert fit to GM70. Probs do that stage 1. Allows for trying different driver bottles. You know, 46, 45, 2a3, 10Y triode idh valves. I’ll probs stick with my triode D3a VA.

Image

Image

Image

Image

Image

Image
"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: 8247
Joined: Mon May 21, 2007 9:42 pm

#4 Re: GM70

Post by Paul Barker »

You can’t tell which is copper, have to lift out one by one: it’s bottom left.
"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: 8247
Joined: Mon May 21, 2007 9:42 pm

#5 Re: GM70

Post by Paul Barker »

As per g2 thread, if anyone can easily afford a vintage gm70 with iron plate to bring to Owston please buy this before it’s bought.

Image
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
User avatar
andrew Ivimey
Oooo, Roberts Radio's sound nice
Posts: 7677
Joined: Mon Jun 11, 2007 8:33 am
Location: Bedford

#6 Re: GM70

Post by andrew Ivimey »

Iron, wow. Why!!!???
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
Paul Barker
Social Sevices have been notified
Posts: 8247
Joined: Mon May 21, 2007 9:42 pm

#7 Re: GM70

Post by Paul Barker »

Ive alreadt bought a spares or repair lab supply after the quash has been imposed on spending. More than my lifes work, but if someone is flush you might never see another. All I know the vintage RCA 211 I have betters the vt4c noticeably. VT46c better than any chinese I had heard up to then, but Ive heard pVane in Gaku On youtube only sadly, but sounded as good as vt4c. I think that pVane are stepping up to the mark.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
User avatar
andrew Ivimey
Oooo, Roberts Radio's sound nice
Posts: 7677
Joined: Mon Jun 11, 2007 8:33 am
Location: Bedford

#8 Re: GM70

Post by andrew Ivimey »

I sold all my vt4cs on. The shavings were gifted!
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
andrew Ivimey
Oooo, Roberts Radio's sound nice
Posts: 7677
Joined: Mon Jun 11, 2007 8:33 am
Location: Bedford

#9 Re: GM70

Post by andrew Ivimey »

Oh for ffffffff's sake..... shavings. Bloody he'll

S h u a g A n forgotten what I'm talking about....
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
Paul Barker
Social Sevices have been notified
Posts: 8247
Joined: Mon May 21, 2007 9:42 pm

#10 Re: GM70

Post by Paul Barker »

oh wow, its not that I dont care about the Ukrane people, but two silver gm70 valve bases and two gm70’s are presently in transit from Ukrane.

if they never arrive I wont be complaining. There are bigger fish to fry over there! Ill take one for the team.

ps Sam is fighting at the biggest event worldwide in Liverpool tomorrow a grapplin contest against The Daisy Crew from usa. its a megga thing. Sam already got gold in Sheffield against all comers in his weight class, its a national event, recently. Has something to do with why hes been selected. He took a team of 5 from his gym three got gold one got bronze. From a flegling gym in little old Scarborough. Theyve got twenty scarborians in a minibus for support, Sam travelling with two of his mentors.

Hope he wins.

Im not well enough to go. The face plant is still holding me to ransom.
"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: 8247
Joined: Mon May 21, 2007 9:42 pm

#11 Re: GM70

Post by Paul Barker »

I got my AVO 8’s out of storage. Ill have to orders AVO batteries!
"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: 8247
Joined: Mon May 21, 2007 9:42 pm

#12 Re: GM70

Post by Paul Barker »

The fuse blowing supply arrived. So far found one Riffa Y cap leaking. Ordered all four X and Y caps exact same models, when theyre fitted Ill try it, AVOS at the ready. Theyll probably arrive next week. Not rushing. But optomistic. The electrolytincks are all testing great. That one Y cap explains it so far! If that fails Ill unsolder the transistors and test them, but visually incirquit they seem fine, and not stressed. If that doesnt fix it Ill just go single monoblock. I want to keep the 801a amp and just leave it alone. I need this amp for comparison anyway.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
JohnG
Old Hand
Posts: 417
Joined: Sat Mar 25, 2017 10:59 am

#13 Re: GM70

Post by JohnG »

I have prior to Covid spent half a day listening to SE GM70 Amps through a system I have been quite familiar with, which uses Horn Speakers with Alpair Drivers and another Speaker from Black Swift Audio, which were their BVR Speakers.
I recollect how the GM70 Amp was quite impressive as I was very familiar with the speakers in use with a SE 300B Amps and PP Amps driving them.
I recall a greater sense of Bass Presence and the Head Room was perceived as being quite different and noticeable.

The SE GM70 Amps are now used with OB's but I have not heard them used with these.
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8247
Joined: Mon May 21, 2007 9:42 pm

#14 Re: GM70

Post by Paul Barker »

Did you know the load, b+ voltage and current ? Because when theyre operated like a 212 theyre almost indistinguishable, particularly the copper plate, but the graphite dont lag far behind. Youre description needs context or comparative like for like otherwise I can’t tell much from it. But thank you?
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
JohnG
Old Hand
Posts: 417
Joined: Sat Mar 25, 2017 10:59 am

#15 Re: GM70

Post by JohnG »

Hi Paul
I am not an EE minded person, I rely heavily on others for support in these matters.
I was offering an encouragement, I made a reference to the Headroom as I have PP 845's in use and the Headroom perception from these amp's is very noticeable, so I recollect being impressed by the SE GM70 perception of Headroom on offer.

These Amp's belong to Stoyan, who is a forum member if I recall correctly, he was keen to go to Owston last year, but my knee injury changed the plans, I am sure he will be helpful if you inquire.
Post Reply