Hi-having been reading a thread on the WD forum about trying GM70 valves in place of 845 in a Mr Liung amp i was wondering if the same could be tried in my 845 power stage ?
I appreciate the heaters are different but is the basic concept sound using the step up transformers that i have ?
The heater transformers i am using each have two centre tapped secondaries 5-0-5. How could (if i could) i get that to produce 20v ?
GM70 time ?
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pre65
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#1 GM70 time ?
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)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
#2
I don't thihnk you could, maybe voltage doubler, but its going to have some huge current spikes. Other than that its just about a simple swap.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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andrew Ivimey
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#4
I did it with toroids, bridge rectifier caps and a resistor, that was easy but HOT! (Tractor days). I think the GM70 sounds better than 845 but imho.
P.S. I tried a voltage doubler because it was easier, didn't notice anything particularly wrong except it didn't sound right. I like AC but realise there are times when only DC will do.
P.S. I tried a voltage doubler because it was easier, didn't notice anything particularly wrong except it didn't sound right. I like AC but realise there are times when only DC will do.
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pre65
- Amstrad Tower of Power
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#5
I was looking at the Nicholas Chua GM70 design and he uses an 18v transformer with bridge,0.5R resistor,two 22000uf caps and a 15mh choke.
Looks relatively simple (like me
),just need a couple of GM70 and bases to play with now.
Looks relatively simple (like me
),just need a couple of GM70 and bases to play with now.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)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
#8
Triode mode Nick.I'm really impressed with how it's sounding at the moment.Mo's been round a couple of times and he rather likes it too.Makes me wonder what a decent circuit and good trannies would sound like.I find the metal-anode 813's far better than the graphites.They're cheap too! 
BTW,I followed your suggestion about the SCR cap,and it looks like they are willing to send a replacement,though understandably they wanted to see the duff one so I've sent it off.We shall see!
Sorry for the hijack Phil.
BTW,I followed your suggestion about the SCR cap,and it looks like they are willing to send a replacement,though understandably they wanted to see the duff one so I've sent it off.We shall see!
Sorry for the hijack Phil.
#9
Good news about the caps Ali, lets hope for the best.
Maybe I should invite myself and the 211 to Leeds some time
Maybe I should invite myself and the 211 to Leeds some time
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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andrew Ivimey
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#11
All roads roam to Leeds, Ali.
But my road is long and winding, A1.
But my road is long and winding, A1.