HV problem on preamp tubes - 2204

[elegost]

Hi folks,

I'm having an issue on my 2204 build.

I'm seeing straight B+ on pins 1 and 6 of my preamp tubes.

After the rectifier i see 510vdc, at pins 1 and 6 i see 495vdc on all three preamp tube sockets (!) with no preamp or power tubes in the amp.

I was seeing proper voltages (280v) there and then I added some 1ohm bias resistors between pin 1 and ground on the power tube sockets so i could measure the bias. I must have screwed something up in the process but I am having trouble figuring out what. The 10k5w resistors on the B+ line seem to be ok when measured in circuit

Any troubleshooting advice would be much appreciated

[sluckey]

Plug in the tubes.

[elegost]

With V1-3 plugged in but no power tubes in i see:

V1 pin 1 - 460
V1 pin 6 - 461
V2 pin 1 - 460
V2 pin 6 - 465
V3 pin 1 - 270
V3 pin 6 - 466

[sluckey]

PLUG IN ALL THE TUBES.

[xtian]

+1. What he's suggesting is that your RC nodes don't drop any (much) voltage until they're under load! This is true of all the amps we typically work on.

[elegost]

Ok will do, sorry about that.

With all tubes in i get the following readings, also, V4 V5 get very hot and V3 gets medium hot, V1 and V2 stay cooler.

V1 - Pin1 452v
V1 - Pin6 451v

V2 - Pin1 453v
V2 - Pin 6 451v

V3 - Pin1 266v
V3 - Pin 6 453v

V4 - Pin 3 483v
V4 - Pin 4 482v
V4 - Pin 5 -54v
V4 - Pin 6 483v

V5 - Pin 3 484v
V5 - Pin 4 480v
V5 - Pin 5 -54v
V5 - Pin 6 480v

Thanks for the help!

[xtian]

Now I agree there's an issue. (Not the part about your power tubes being hot, though. They will normally be hot enough to burn you.)

Preamp tubes might not be drawing current because there's an error in wiring. Make sure the cathode resistors are actually grounded. Double and triple check each connection against the schematic.

Is this your first build?

Post some photos, and I'll help you look.

[elegost]

Ok here are a bunch of shots, thanks for the help.

Yes, first amp i'm afraid so potential for dumb mistakes is high.

Let me know if there's anything you'd like better shots of or would like me to test. Cathode resistors appear to be grounded as far as I can tell. I will check the cathode resistors and work through the schematic again.


[img1224]http://i.imgur.com/UrfCwaM.jpg[/img]

[img1224]http://i.imgur.com/Ru8hoGx.jpg[/img]

[img1224]http://i.imgur.com/gxsa2s8.jpg[/img]

[img1224]http://i.imgur.com/6nokP7n.jpg[/img]

[img1224]http://i.imgur.com/2Eoi2zh.jpg[/img]

[img1224]http://i.imgur.com/hSqQ8Y5.jpg[/img]

[img1224]http://i.imgur.com/TtYhnsp.jpg[/img][/img]

[elegost]

Ok so i think I found a sketch joint on the v3 cathode so i reflowed it and voltages look better! You rule Xtian!

[xtian]

Nice work on the build! Keep us informed.

Is that a Mojotone kit?

[elegost]

Thanks!

Yes it's the Mojotone "British 800 50w" kit.

[sluckey]

Is it working now?

[SilverFox]

That's a very nice first build. How did you get the assembly experience?

silverfox.

[elegost]

Yes it's working now!
I will post clips after I get back from a summer trip.
Sounds good, a bit trebly, and it's ball-crushingly loud, both of which I expected.
I am going to do a series of mods to it now, which was always the plan.

Thanks for the complement! I've done some little projects before, a distortion box, an O2 headphone amp, and I spent a LOT of time reading ampgarage, metroamp, and the sloclone forum.

[rp]

Pretty nice first attempt. Time to set aside a wall for your future amps.