GM70 SET
-
- Thermionic Monk Status
- Posts: 5643
- Joined: Thu May 24, 2007 11:22 am
- Location: People's Republic of South Yorkshire
#61
Another 4 (nearly 5) months pass but I've had a concerted effort the last couple of evenings since Owston and we have ignition!
The voltages look to check out okay from the quick look I had before I made tea. Something was smelling rather hot though so close scrutiny is required. I've only hooked it up to cheap speakers to test but it makes the right sort of noises which is encouraging .
At least one of the transformers buzzes a bit though, might be the filament transformers, and I can feel vibration in the first choke of the LCLC power supply. I haven't snubbed it yet but would it be worth trying a 100nF cap in front of it?
I don't know what it sounds like yet but I have to say I could fall in love with GM70s just for how they look. Just a shame my energy consumption meter was reading 370W!
The voltages look to check out okay from the quick look I had before I made tea. Something was smelling rather hot though so close scrutiny is required. I've only hooked it up to cheap speakers to test but it makes the right sort of noises which is encouraging .
At least one of the transformers buzzes a bit though, might be the filament transformers, and I can feel vibration in the first choke of the LCLC power supply. I haven't snubbed it yet but would it be worth trying a 100nF cap in front of it?
I don't know what it sounds like yet but I have to say I could fall in love with GM70s just for how they look. Just a shame my energy consumption meter was reading 370W!
- IslandPink
- Amstrad Tower of Power
- Posts: 10041
- Joined: Tue May 29, 2007 7:01 pm
- Location: Denbigh, N.Wales
- Dave the bass
- Amstrad Tower of Power
- Posts: 12276
- Joined: Tue May 22, 2007 4:36 pm
- Location: NW Kent, Darn Sarf innit.
#63
Phwwwwwwwwwwwooooooooooooaaaaaaaarrrrr!
2 Rev counters too!
Or 'Notes per minute' ala Nigel Tuffnel?
DTB
2 Rev counters too!
Or 'Notes per minute' ala Nigel Tuffnel?
DTB
"The fat bourgeois and his doppelganger"
-
- Thermionic Monk Status
- Posts: 5643
- Joined: Thu May 24, 2007 11:22 am
- Location: People's Republic of South Yorkshire
#64
Currently reading 0 notes per minute as they're not hooked up to anything at the moment. I couldn't resist them when I saw them, I thought they might go well with the GM70s .
#66
same question here....thomas wrote:And another congratulations!
So are those filament heatsinks meaty enough?!
Cheers!
T
what is the supply circuit to the coleman regs?
and another congrats too!
There's nowhere you can be that isn't where you're meant to be
- pre65
- Amstrad Tower of Power
- Posts: 21399
- Joined: Wed Aug 22, 2007 11:13 pm
- Location: North Essex/Suffolk border.
#67
Nice one Simon. Let us know how you like the sound.
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)
- Dave the bass
- Amstrad Tower of Power
- Posts: 12276
- Joined: Tue May 22, 2007 4:36 pm
- Location: NW Kent, Darn Sarf innit.
#68
If it's that choke-loaded 12GN7 -> GM70 that our-Popz built it should be yummy. His was great (IMO).
DTB
DTB
"The fat bourgeois and his doppelganger"
- Cressy Snr
- Amstrad Tower of Power
- Posts: 10581
- Joined: Wed May 30, 2007 12:25 am
- Location: South Yorks.
#69
Good stuff Simon.
Ought to be boxed up and ready by the next Owston then?
Ought to be boxed up and ready by the next Owston then?
Sgt. Baker started talkin’ with a Bullhorn in his hand.
- Cressy Snr
- Amstrad Tower of Power
- Posts: 10581
- Joined: Wed May 30, 2007 12:25 am
- Location: South Yorks.
#70
Yes I thought that GM70 of Phil's was a great sounding piece of kit.Dave the bass wrote:If it's that choke-loaded 12GN7 -> GM70 that our-Popz built it should be yummy. His was great (IMO).
DTB
Better than the 833A (sorry Phil)
Doris Day was in the room with us.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
-
- Thermionic Monk Status
- Posts: 5643
- Joined: Thu May 24, 2007 11:22 am
- Location: People's Republic of South Yorkshire
#71
Now that's very funny Steve . When was the last time I put something in a box? I have had severe words with myself since the last Owston and I'm full of good intention but somehow I can never bring myself to say yep, it's finished. I will redouble my efforts.SteveTheShadow wrote:Good stuff Simon.
Ought to be boxed up and ready by the next Owston then?
Yep it's 12GN7 very close to Nicholas Chua's circuit. Hearing Andrew's amp last Owston was good enough for me. I've only got 480V across the B.c. and I'd like a bit more really, but I'm working with the iron I have.
The raw DC supply is choke input as per Rod's design. Hammond 185something trafo into 0.0025R cap choke cap. The amp hasn't been on long enough yet to know hot the heatsinks fare. I haven't even set the voltage with HT applied yet. Something was getting rather warm though, might just be the vitreous enamel resistor breaking in. I hope.
Last edited by simon on Thu Nov 14, 2013 5:57 pm, edited 1 time in total.
- Mike H
- Amstrad Tower of Power
- Posts: 20189
- Joined: Sat Oct 04, 2008 5:38 pm
- Location: The Fens
- Contact:
#72
simon wrote:Currently reading 0 notes per minute as they're not hooked up to anything at the moment.
I've got two like that I must use really.
SteveTheShadow wrote:Doris Day was in the room with us.
Very good Simon congrats
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
-
- Thermionic Monk Status
- Posts: 5643
- Joined: Thu May 24, 2007 11:22 am
- Location: People's Republic of South Yorkshire
#73
Aye, Steve makes it sound like that was a good thing .
I've snubbed the first choke with a couple of 220nF caps but it hasn't made any difference to the vibration. Not too keen on that, just doesn't feel good to me.
I can report thought that after about an hour the heatsinks are only a little warm to the touch. I think I've got a better idea where the hot smell might be coming from. The GM70s give off a surprising amount of heat, but more concerning are the dropper resistors to the driver decoupling cap. I've mis-rated them - there's 8W through them and they're only 14W rated. Good job it's on a breadboard. Really they should have been paralleled 30k 14W. I could use a couple of 0A2s but goes against what I'd like to keep as essentially a simple amp.
So how does it sound? I've only heard it on the cheap bookshelf speakers upstairs so far which are fairly mid-fi but it does seem to be rather beguiling with a pleasant ease. So far so good.
I've snubbed the first choke with a couple of 220nF caps but it hasn't made any difference to the vibration. Not too keen on that, just doesn't feel good to me.
I can report thought that after about an hour the heatsinks are only a little warm to the touch. I think I've got a better idea where the hot smell might be coming from. The GM70s give off a surprising amount of heat, but more concerning are the dropper resistors to the driver decoupling cap. I've mis-rated them - there's 8W through them and they're only 14W rated. Good job it's on a breadboard. Really they should have been paralleled 30k 14W. I could use a couple of 0A2s but goes against what I'd like to keep as essentially a simple amp.
So how does it sound? I've only heard it on the cheap bookshelf speakers upstairs so far which are fairly mid-fi but it does seem to be rather beguiling with a pleasant ease. So far so good.
- andrew Ivimey
- Social Sevices have been notified
- Posts: 8318
- Joined: Mon Jun 11, 2007 8:33 am
- Location: Bedford
#74
Snubbers are bollocks! ducks ...
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.