Fender Dlx Rev build- last Q b4 fire-up.

[Sea Chief]

Ive used the Cltr recently too and works as expected. Looked inside hoping to see s'thing amiss.. nothing. All solid as before, nothing physically possible amiss to how it was a few months ago.

[eschertron]

Ok 1st test done. I read 50.9v at both pin 5's of V7,V8 (6v6's).. ok that's good..

But the 100w light bulb didnt light. WTF? (Light checked, 2nd one too, switches to ON, plug in normally to wall=bright, plug into my C.ltr and nothing whilst checks done/ nothing before either).

If the voltages in the amp look normal, it can be reasonable that the light bulb limiter doesn't draw enough current to become even visibly bright (or dim, however you think about it). With good bias voltages - pins 5 will be NEGATIVE 50-ish volts compared to ground - add the tubes and then the recto might pull enough current to dimly light the bulb. anything more than dim is bad
At that point you can check all the B+ voltages through the amp to see that the power supply is working. As stated above, the voltages won't be "spec" with the limiter, but will be indicative of the health of the unit.

[Sea Chief]

My C.LTR wiring: using a simple, rewired 2 way mains cable extension block:

The GND terminals of the 2 sockets joined.
The LIVE (brown here) wire goes to 1st socket's usual LIVE terminal. Ends here/ does not continue to 2nd socket.
The NEUTRAL (blue here) wire goes to the 2nd socket's usual NEUTRAL terminal. Ends here/ does not continue to 1st socket.
A link joins the NEUTRAL terminal of 1st socket.. to the LIVE terminal of 2nd socket.

I plug light into 1st, amp into 2nd. I also switched around fwiw. (Light's own switch defo ON ready beforehand/ checked b4).

[Sea Chief]

If the voltages in the amp look normal, it can be reasonable that the light bulb limiter doesn't draw enough current to become even visibly bright (or dim, however you think about it). With good bias voltages - pins 5 will be NEGATIVE 50-ish volts compared to ground - add the tubes and then the recto might pull enough current to dimly light the bulb. anything more than dim is bad
At that point you can check all the B+ voltages through the amp to see that the power supply is working. As stated above, the voltages won't be "spec" with the limiter, but will be indicative of the health of the unit.

But even if the bulb was so dim its not visibly bright.. wouldnt I 1st expect to see it (as I was expecting) to be 100w bright before I > turn on/ & then stby too > and hopefully go down to dim-? this is what Ive always seen using this C.ltr (albeit Ive never done this specific -50vdc bias check before).

[eschertron]

My C.LTR wiring: using a simple, rewired 2 way mains cable extension block:

The GND terminals of the 2 sockets joined.
The LIVE (brown here) wire goes to 1st socket's usual LIVE terminal. Ends here/ does not continue to 2nd socket.
The NEUTRAL (blue here) wire goes to the 2nd socket's usual NEUTRAL terminal. Ends here/ does not continue to 1st socket.
A link joins the NEUTRAL terminal of 1st socket.. to the LIVE terminal of 2nd socket.

That's just what I have! It also doubles as a current sensor, when I take the lamp out of the one plug and insert a loop (or a coil of ten loops, for better sensitivity) into the plug. This allows me to read the current draw of the unit using my amp meter.

[eschertron]

But even if the bulb was so dim its not visibly bright.. wouldnt I 1st expect to see it (as I was expecting) to be 100w bright before I > turn on/ & then stby too > and hopefully go down to dim-? this is what Ive always seen using this C.ltr (albeit Ive never done this specific -50vdc bias check before).

Why would the bulb be bright? That indicates a short-circuit somewhere... unless I've lost what you were doing?
Maybe the bulb bright for a fraction of a second at powerup?

[Sea Chief]

Why would the bulb be bright? That indicates a short-circuit somewhere... unless I've lost what you were doing?
Maybe the bulb bright for a fraction of a second at powerup?

What Im used to, you see (why anything other to this is strange to me).. is when I turn on amp the bulb goes bright for 1,2 seconds then fairly rapidly decreaces to dim.

So the bias test Ive done using the C.ltr is ok/ the C.ltr is working as expected? (albeit I read 50vdc not -50vdc as was I assume actually on the DMM).

I want to make sure the C.ltr is ok before I continue you see.. or there's the chance it will not do its primary job of protecting, should there be any shenanigans.

[eschertron]

What Im used to, you see (why anything other to this is strange to me).. is when I turn on amp the bulb goes bright for 1,2 seconds then fairly rapidly decreaces to dim.

Ah! But that's with all the tubes in, innit?

[eschertron]

So the bias test Ive done using the C.ltr is ok/ the C.ltr is working as expected? (albeit I read 50vdc not -50vdc as was I assume actually on the DMM).

Don't assume... Reversing the diodes/caps/whatnot in the bias supply is a very easy mistake to make. You may want to check again

[Sea Chief]

Don't assume... Reversing the diodes/caps/whatnot in the bias supply is a very easy mistake to make. You may want to check again

[Yes with tubes innit, innit. Ok yes yes I see the process clearer already! (electronics is still a different language even still tbh)].

Check again point noted/ a good rule of thumb. Here though as its a pcb fender board I can assume they are in correctly, & I just didn't read the '-' before (again, not used to seeing a - before DMM numbers).

Ok so what's next? I load up all tubes, and simply switch on (with a spkr load in of course) expecting/ hoping just to observe a dimming of the bulb-?

Thx eschertron.

[Sea Chief]

Ok good news!

Done test 2: all tubes in and turn ON 1st time.. bulb goes bright then asap to dim. Then after 1m, STBY switched.. bulb slightly brighter then back to same dimmness.

Woohoo! It lives. No horrible noises from spkr either- dead quiet in fact.

[Sea Chief]

I guess its Voltage readings now. What the procedure, V1 to V9? and which pins?

And how do you guys do the readings.. amp continually on, and carefully probe one point/ note, then onto the next etc? or do you turn off between each reading (to disconnect the probe)-?

Most aprreciated, Sea Chief.

[Sea Chief]

Don't assume... Reversing the diodes/caps/whatnot in the bias supply is a very easy mistake to make. You may want to check again

B+ read at TP1 on th schematic (on the terminal at CP14 to be precise).. and I get 487v! blimey that's high eh? (396vdc expected/ noted on the TP1 schematic).

It also went to 700v before I flipped STBY. Is that right??

[Chuck H]

What is the nature of your power supply? Are you using a DR power transformer? Are you using a rectifier tube? If not, are you using a full wave or bridge type rectifier?

There are a lot of rough ideas about "proper" voltage for DR's WRT power transformers. Some seem to think that the PT should produce HV such as an original were plugged into modern AC mains. Others try to match what the original voltage would have been with 1965 AC mains. Still others seem to hit wide on one front or the other.

Any info on your actual PT and how you have the power supply wired would be helpful now.

[Sea Chief]

B+ at TP1= 487v

V8 (6v6gt) pin 3= 478v
V7 (6v6gt) pin 3= 478v

V1 pin 1= 193v

Ok so a few readings to start there, & look worryingly high. (95vtoo high to the 391v TP1 figure on shematic!?!).

But I had to have a brief play once I found a ballpark ok figure for V1 pin 1........ and it sounds good! so Im pleased. Its nice and quiet, it seems not unusually hot anywhere, no tubes glowing OTT red. A loud pop on turn off tho but hey.

Enough for today: will be looking fwd to reading any comments chaps esp the high voltage.
Hugely grateful, Sea Chief.