Firing up Poseidon without driver tubes

for Dynaco Mark II/III/IV and DIY PP monoblocks

Firing up Poseidon without driver tubes

Postby Blair » Mon Nov 03, 2008 4:16 pm

Ii is OK to fire up this circuit with no driver tubes isn't it? Just to make sure everything else is OK. I'm waiting on my driver sockets to arrive, but have everything else complete.

Thanks,

Blair
Blair
KT88
 
Posts: 1272
Joined: Thu Nov 09, 2006 10:22 am

Postby Ty_Bower » Mon Nov 03, 2008 5:09 pm

I'd fire it up with no tubes at all, and verify you have correct negative bias voltage at pins 5 and 6 of the KT88 sockets. Then if you want, you can probably run it with the KT88 and the rectifier installed, and no driver tubes.

I seem to recall this question was asked before, maybe in the ST70 forum? I think the answer was that it is OK to run with both driver tubes out. If you leave one of them in (can't remember which one, probably the 12AU7) the circuit will oscillate and squeal.
User avatar
Ty_Bower
KT88
 
Posts: 1494
Joined: Wed Mar 21, 2007 2:50 pm
Location: Newark, DE

Postby Blair » Mon Nov 03, 2008 6:06 pm

Thanks Ty,

This one is a bit different. It is a SS rectified amp, so it is best to have the tubes in to present a little load on the PS or else it can be a bit high. 560v+ ish. I'd feel better having the tubes in if it is OK to do this with no driver tubes.

What do you think?

Blair
Blair
KT88
 
Posts: 1272
Joined: Thu Nov 09, 2006 10:22 am

Postby Ty_Bower » Mon Nov 03, 2008 6:39 pm

Ah yes, I remember that amp now.

Aren't those PSU caps rated for 600V? What's the rating on your coupling caps on the Poseidon board? How hard is it to disconnect the bridge rectifier? I'm reading the other thread going on in Poseidon, and sympathizing what can happen if the bias supply isn't working when the B+ comes on.

I'll try to search out the thread discussing Shannon's Poseidon/ST70 circuit, and what happens with no driver tubes.
User avatar
Ty_Bower
KT88
 
Posts: 1494
Joined: Wed Mar 21, 2007 2:50 pm
Location: Newark, DE

Postby Blair » Mon Nov 03, 2008 6:50 pm

This post is mostly insurance. I have had this amp up and running before with a perfectly good bias supply and everything, but cannot remember for the life of me if I ever ran it with no drivers. I have a quad of 6L6Gcs I can spare even though they are brand new. No more use for them after this. No more projects for a long time, or at least until my wife and I figure out how things will be with a baby.

Thanks for all your help Ty, and yes the PS caps are all rated at 600v after being wired in series. They are 410uf at 300v each. I used 100K bleeders, so there is some load even with no tubes, but I would not figure it is enough to keep the B+ down.

Blair
Blair
KT88
 
Posts: 1272
Joined: Thu Nov 09, 2006 10:22 am

Postby Blair » Mon Nov 03, 2008 9:33 pm

Here is the new build minus the noval sockets.

Image

http://img.villagephotos.com/p/2005-12/1115293/CannonCamera184.jpg
http://img.villagephotos.com/p/2005-12/1115293/CannonCamera182.jpg
http://img.villagephotos.com/p/2005-12/1115293/CannonCamera183.jpg

The sockets will be recessed so the base of the tubes are just below the top plate. You can see the PS mods. I went with a FWB on each set of HV secondaries, abd each channel now has 820uf of capacitance. Hopefully this improves the small sag I was hearing in the bass response. The tubes in the amp are those Sovtek 6L6GCs. That is why they look so small.

Blair
Blair
KT88
 
Posts: 1272
Joined: Thu Nov 09, 2006 10:22 am

Postby Ty_Bower » Mon Nov 03, 2008 9:41 pm

Beautiful woodwork. I need to get you to build me a couple bases for my amps. All I know how it do is 2x4 pine held at the corners with lag bolts.

Dumb question, though - do you have to flip the beast up on edge to adjust the bias balance pots on the Poseidon boards?
User avatar
Ty_Bower
KT88
 
Posts: 1494
Joined: Wed Mar 21, 2007 2:50 pm
Location: Newark, DE

Postby Blair » Mon Nov 03, 2008 9:47 pm

LOL!! Yellow_Light_Colorz_PDT_04

Yeah, I do. Unfortunately, I did not think of that before I finished drilling all the holes in the top plate. I was kicking myself, but I'm afraid driling another hole would ruin the paint job. Any ideas?

Blair
Blair
KT88
 
Posts: 1272
Joined: Thu Nov 09, 2006 10:22 am

Postby Ty_Bower » Mon Nov 03, 2008 10:06 pm

deicide67 wrote:Any ideas?


Buy matched pairs? Yellow_Light_Colorz_PDT_09
User avatar
Ty_Bower
KT88
 
Posts: 1494
Joined: Wed Mar 21, 2007 2:50 pm
Location: Newark, DE

Postby Blair » Tue Nov 04, 2008 8:10 am

I do buy matched quads every time I purchase new tubes, but your comment got me thinking last night about why I can't make this happen, and there is really no reason. All I will have to do is drill a 3/8-1/2" hole beside the 12AU7 and insert a grommet. It may look a little odd having a hole there, but not too bad. I just do not know how to line up the hole with the adjustment screw or else I would go with a smaller hole. It should work, and I have nothing better to do while I wait for my sockets.

Blair
Blair
KT88
 
Posts: 1272
Joined: Thu Nov 09, 2006 10:22 am

Postby TomMcNally » Tue Nov 04, 2008 1:50 pm

Blair -

You don't have to stick with the little board mounted pots.
You can pull them off and replace them with any 500K
linear pots, with a different mounting method.
You could could even mount them side by side on a
small piece of perf-board and mount them in an
easy to get to spot.

... tom
User avatar
TomMcNally
Darling du Jour
 
Posts: 2729
Joined: Sat Nov 19, 2005 2:19 pm
Location: Northfield, NJ

Postby Blair » Tue Nov 04, 2008 2:02 pm

Thanks Tom.

Funny you posted that because I was thinking the same thing. There is plenty of room. I'd still like a nice multi-turn pot for this, but mounted below the top plate so wandering hands cannot adjust the setting. Do you know of a good source for multi turn pots?

Blair
Blair
KT88
 
Posts: 1272
Joined: Thu Nov 09, 2006 10:22 am

Postby TomMcNally » Tue Nov 04, 2008 2:06 pm

Mouser has way too many choices ... anything will work as
long as it's 500K and linear ... I think those trimpots are
something like 1/10th of a watt ?
User avatar
TomMcNally
Darling du Jour
 
Posts: 2729
Joined: Sat Nov 19, 2005 2:19 pm
Location: Northfield, NJ

Postby Blair » Tue Nov 04, 2008 2:08 pm

Thanks Tom. I'll look around for something preferred.

Blair
Blair
KT88
 
Posts: 1272
Joined: Thu Nov 09, 2006 10:22 am

Postby Blair » Thu Nov 06, 2008 10:22 am

Ty answered this in another post of mine by showing me a link and explaining it to me, but I wanted to post this picture to make sure this will work before adding a bunch of wires, and drilling another couple of holes in my amp.

Will this work?

Image

Thanks,

Blair
Blair
KT88
 
Posts: 1272
Joined: Thu Nov 09, 2006 10:22 am

Next

Return to poseidon

Who is online

Users browsing this forum: No registered users and 7 guests

cron