New 100w/HRM build-problems solved

[moj067]

Well it powers up, all filaments light, fender lamp works(blue).
I get around 470v on B+1 which work itself down to 320v on B+5.
All cool w/ me so far.
I'm going no FET input so grounded a 150k to last node for proper drawdown.
Anyway I plug in instrument and no sound...nada.
So, I check my plate voltages.
V1a-214vdc b-205
V2a-345v b-205
v3a-345v b-327
V2 is way wrong I know and it's the plate side where the HRM board hooks up after the 120k resistor. I checked the board and everthing seemed ok.
Anyways took some pictures as they can show what I can't seem to see.
Thanks a bunch already to Funk,Gil,Dogears,MDROBERTS,Norm,Heistl and everyone else whom contributed their picts and layouts.
These amps are frustrating at times but soooo worth it.
*Edit on 07/31/08: Newer pics uploaded
Voltages further down thread apply to this iteration.

[ic-racer]

Do you have enough wires connected to the OD relay board (you probably do, but I can't see anything else to comment on ).

Any signal from the 'send' jack?

What is the cathode voltage on V2a??

[dogears]

A couple suggestions.....

Since you have about 470V of B+, I'd make sure your PI dropping resistor is in the 4.7K to 6.8K range. Shoot for 300-310V on PI plates. Definately don't go lower than 3.3K as the big man in these amps did not. I have seen 8.2K there on amps with big B+

The grid resistor on OD2 is a 150K and not the 180K you used. 180K works, but try the 150K. In this non Bluesmaster circuit, I prefer it.

As for the voltages.... I had this happen when the tube pins and/or socket was loose. Try bending the pics out a little and/or tightening the socket. The tube is not drawing any current so there is no drop across the plate. Straightening the tube pins fixed it for me.

Your B+ is a bit high. With precision power string, you should have 180-190 on V1 and 210-215 or so on V2. Raise the PI drop.

[heisthl]

For starters, make sure the power amp in jack works. if so cliplead from preout to pwramp in, if no sound next eliminate the relay by using a cliplead from V1B coupling cap to the top of the master. Situations like this are where a scope or a signal tracer really helps.

[talbany]

Make sure it's on the clean channel try running a Jumper from the .047 coming out of V1b over to the input to the phase inverter.. This way you can rule out the clean channel and the out put section.. If it works you can work your way back though the loop and master volume.. If all works Ok put the jumper at the input to the OD and switch channels..If that works OK check your switching network... My guess is @ 345 on V2a your OD is not working or at least sounds like crap you will no doubt have to nail that down.. Double check and make sure that side of the tube is biasing up right.. Good Luck


Tony VVT

[moj067]

Thanks to all for suggestions. I 'm still getting lopsided voltages on the A side of V2,the cathode voltage is like 3.53v on pin 3. I'm going to rework my power section to the way the big guy did- I went w/ another method and shouldn't have strayed.
I'm getting 11.3vdc on the left leg of my presence pot, which now that I'm looking at things shouldn't be bridged w/ the center lug at all.
So I'm getting thes same voltage(11.3v) at the entrance of the tantalum cap.
I don't know if thats normal.
I'll check in again after all changes are made.

['67_Plexi]

V2b is simply not conducting.

First check you haven't misread the cathode resistor value for one 10 or 100 times higher or the plate resistor for a value 10 times lower. Check them then check them again. This is by far the most common cause of this issue. I own several of those T-Shirts.

If they are OK, check all the cathode connections right through from the tube socket, through the cathode resistor/cap and especially check that the cathode network is grounded.

Also check that you have HT on plate pin and not a dry solder joint or a bad pin on the socket. Also make sure one of your tube pins hasn't bent 90 deg. Thats happened to me more times than I'd like to admit.

Hope you find the cure.

[ic-racer]

Thanks to all for suggestions. I 'm still getting lopsided voltages on the A side of V2,the cathode voltage is like 3.53v on pin 3. I'm going to rework my power section to the way the big guy did- I went w/ another method and shouldn't have strayed.
I'm getting 11.3vdc on the left leg of my presence pot, which now that I'm looking at things shouldn't be bridged w/ the center lug at all.
So I'm getting thes same voltage(11.3v) at the entrance of the tantalum cap.
I don't know if thats normal.
I'll check in again after all changes are made.

Let me see if I am following correctly. Your V2A plate is 345v and the V2A cathode is 3.53v

If that is the case , then the tube is conducting. Somehow you are getting too hot of a B+ voltage on that tube. I can't figure that out because V2A & V2B should share the same B+. As pointed out, perhaps a 10x smaller plate value was inadvertently used??

['67_Plexi]

Thanks to all for suggestions. I 'm still getting lopsided voltages on the A side of V2,the cathode voltage is like 3.53v on pin 3. I'm going to rework my power section to the way the big guy did- I went w/ another method and shouldn't have strayed.
I'm getting 11.3vdc on the left leg of my presence pot, which now that I'm looking at things shouldn't be bridged w/ the center lug at all.
So I'm getting thes same voltage(11.3v) at the entrance of the tantalum cap.
I don't know if thats normal.
I'll check in again after all changes are made.

Let me see if I am following correctly. Your V2A plate is 350v and the V2A cathode is 3.53v

If that is the case , then the tube is conducting. Somehow you are getting too hot of a B+ voltage on that tube.

OK...barely conducting if you wish to be pedantic. I still suspect a resistor value.

[moj067]

Working on it, the connections for cathode to ground have continuity. Swapped out tubes, checked plate voltage, now after reading your responses I'm gobsmacked w/ the question,"why didn't I just check continuity through the pin?"Doh! I think I don't want to think the socket is bad because these are some nice NOS sockets and are solid as I've seen, but you never know huh? Still changing over output section to more familiar wiring scheme for these amps. Just being patient w/ the process and trying not to get too frustrated. Thanks all! Will post follow up picts to lay more breadcrumbs for those behind me.

['67_Plexi]

Working on it, the connections for cathode to ground have continuity. Swapped out tubes, checked plate voltage, now after reading your responses I'm gobsmacked w/ the question,"why didn't I just check continuity through the pin?"Doh! I think I don't want to think the socket is bad because these are some nice NOS sockets and are solid as I've seen, but you never know huh? Still changing over output section to more familiar wiring scheme for these amps. Just being patient w/ the process and trying not to get too frustrated. Thanks all! Will post follow up picts to lay more breadcrumbs for those behind me.

A lot of NOS parts suffer from tarnish on the metallic connections, tube sockets are rampant for it. I wouldn't thank you for giving me NOS tube sockets, there's less chance of a brand new tube socket failing than a 'good ole' NOS one thats been stored in some box in some humid warehouse taking on moisture for the last 30 years.

Did you double check those resistor values ?

[glasman]

I had a a couple of amps have similar issues.

One was caused by a bad cathode connection.

The second because the filament was only working on one half of the 12AX7. Bad connection on Pin 4 as I remember now....

[moj067]

Yep, I checked those resistor values aaaaand you were right Alan, I owe a pint or something. Thanks aplenty, I put in what to my crappy eyes at the time looked to be 2.7k when as you summized was 27k. I'm still finishing up the streamling of my power section arrangement ( I like it better already) and will follow up w/ what should be positive results. I'm now filled w/ guarded optimism, I think my P.I. dropping resistor will have to come up in value though, as Scott recommended. I will listen first before changing the 180k to 150k on the OD2 resistor, but I'm sure Scott is probably right on.
Thanks to all for your interest as I muddle through this fun build.

[dogears]

Good catch!

Definately try the 150K. That is the defacto standard grid resistor on Skyline non Bluesmaster HRM amps. The real ones and not some net schematic.....

Yep, I checked those resistor values aaaaand you were right Alan, I owe a pint or something. Thanks aplenty, I put in what to my crappy eyes at the time looked to be 2.7k when as you summized was 27k. I'm still finishing up the streamling of my power section arrangement ( I like it better already) and will follow up w/ what should be positive results. I'm now filled w/ guarded optimism, I think my P.I. dropping resistor will have to come up in value though, as Scott recommended. I will listen first before changing the 180k to 150k on the OD2 resistor, but I'm sure Scott is probably right on.
Thanks to all for your interest as I muddle through this fun build.

[ic-racer]

First check you haven't misread the cathode resistor value for one 10 or 100 times higher

Good!