~210V but I'm seeing 460V

My first thought is no plate current is flowing in that tube.
What do you measure on the cathode (pin 3) of that tube? Should be about 2VDC.

 

The voltage really jumps around quite a bit on pin 3. It ranges from 1.6 VDC to 2.8VDC.

 

Schematic

https://cdn.shopify.com/s/files/1/2325/2729/files/Deluxe-Reverb-AB763-schematic.pdf?5926397210715640943

Layout

https://cdn.shopify.com/s/files/1/2325/2729/files/Deluxe-Reverb-AB763-layout.pdf?5926397210715640943

Make sure the lead from the doghouse is on the left side of the 220k. Also make sure the 220K is correct. Could be a 22k and not doing it’s job.

Also, make sure the lead from pin 7 is going to the right point with a continuity test.

Actually, make sure everything on the vibrato section is in the right place. Make sure both the left and middle tab of the speed pot are grounded by the 100-120k resistor.

 

Schematic

https://cdn.shopify.com/s/files/1/2325/2729/files/Deluxe-Reverb-AB763-schematic.pdf?5926397210715640943

Layout

https://cdn.shopify.com/s/files/1/2325/2729/files/Deluxe-Reverb-AB763-layout.pdf?5926397210715640943

Make sure the lead from the doghouse is on the left side of the 220k. Also make sure the 220K is correct. Could be a 22k and not doing it’s job.

Also, make sure the lead from pin 7 is going to the right point with a continuity test.

Actually, make sure everything on the vibrato section is in the right place. Make sure both the left and middle tab of the speed pot are grounded by the 100-120k resistor.

View attachment 471316

I have verified the 220K resistor more than once (I measure each resistor before it goes on the board but this doesn't mean I haven't made this mistake!).

I can verify that the lead from pin 7 originates from the correct location (continuity tested on completion and again now - I dot these as in the image below.

I can verify that there there is a 100k resistor connected to ground bus from lugs 2 and 3 of the (3M RA) speed pot.

Thanks for the drawings! They are bit clearer than the Fender ones I was using (pin 1 should be 270 V).

 

 

Oddities will occur when plate voltages exceed 350VDC on 12AX7s...460VDC on an active 12AX7 would do it.
How much voltage is dropped across the 220KΩ plate resistor?

 

The voltage drops from 475V to 382V. That said, the voltage really jumps around a lot on

I am curious about the coiled, red-insulated wire in the image.
View attachment 471327

The coiled red wire is not connected to the circuit. It is merely extra shielding around the three (twisted) wires coming out of the doghouse. The idea (according to my research - this wasn't my idea) was to shield those wires from the wiring that goes up to the pots in the vibrato channel preamp section. I cannot say to what extent this may or may not be effective since this is the first time I have done it and I don't yet have a fully functional circuit. That said, a primary goal is to make these amps as quiet as possible (which is very challenging in channel 2 of the DR).

 

I am curious about the coiled, red-insulated wire in the image.

 

Update: I swapped out some tubes. Moved a (known working) 7025 into V4 and put in a different (known working) 12AX7 into V5. No discernible difference.

 

Here's a link to video/audio of what i am hearing and seeing:

IMG_0749.MOV

drive.google.com

As an aside, when I go to drain the caps at the B+1 junction, I am seeing a bit of an arc (wee spark). That can't be good, of course, but I am concerned that it might mean something that I haven't the experience to ascertain.

 

As an aside, when I go to drain the caps at the B+1 junction,

What value of discharge resistance are you using?
Reservoir or filter caps in most deluxe-sized tube amps, store immense amount of electrical energy. If the resistance to ground is low, she's going to spark, at those high voltages.

 

very nice work.
perhaps new 2.7k and 25/25 on cathode

 

I can give that a try. I have meetings for the next couple hours but I'll jump on this asap.

 

this is my power cap bleeder...the resistor keeps the pop(which can be startling and cause a hand reaction that brings a shock) and fast draining to a minimum

 

this is my power cap bleeder...the resistor keeps the pop(which can be startling and cause a hand reaction that brings a shock) and fast draining to a minimum

I'm using the same resistor with a slightly different design.

 

Turn down the trem speed and depth (or use the footswitch jack). Does the voltage stabilize?

 

I find that I have to turn both up to max to get a somewhat stable reading.

 

a full set of pics showing your entire good work, knighthawk, is porn for some of us...

 

Oh, I know exactly what you mean!
As requested...

 

Incidentally, I swapped out the 220K and reflowed both sides of the connection (reseated the 10 meg as well).

Nothing new to report. Still screams at 2 on the volume pot and sounds like I'm tuning in a top 40 station from Neptune.

Edit: On the upside. Channel 1 sounds pretty much like ti should.

 

may be off base here.....you describe what could result from a reversed feedback loop...unsolder the 820R running from the speaker jack tip(where yellow meets green) to the post pi network and listen for a difference....cant hurt to try...if it is improved then switch the speaker jack wires(the green and black) from the output tranny and rehook the feedback loop(the 2nd channel has an extra triode in use and the signal is inverted from the normal channel).
this should not affect the V4 pin 1 voltage issue....still..

 

may be off base here.....you describe what could result from a reversed feedback loop...unsolder the 820R running from the speaker jack tip(where yellow meets green) to the post pi network and listen for a difference....cant hurt to try...if it is improved then switch the speaker jack wires(the green and black) from the output tranny and rehook the feedback loop(the 2nd channel has an extra triode in use and the signal is inverted from the normal channel).
this should not affect the V4 pin 1 voltage issue....still..

I'm willing to give this a try but I'm not sure exactly how to do what you are suggesting.

You want me to unhook the 820R and hook the speaker jack directly it into the 47ohm/22k ohm/.1uf shunt cap junction?

Question: Would that not invert channel 1?

 

glad you are making progress.
the feedback loop may be moot now: some enjoy a switch to close or open the loop and call it a "tweed" switch

 

Interesting. I need to know all about this now. I will definitely research this and give it a shot. Will let you know how it turns out.

 

Not sure if anyone is interested or not but just in case:

Sharing my parts list for this build...

Item	Brand/Source	COST	SOURCE
Power Transformer	Hammond 291BX	$163.99​	Hammond 291BX - Power Transformer UPGRADE UPGRADE for (Deluxe, 5A3, 5B3, 5C3, 6G3, AB763) (Deluxe Reverb, A1172, A1270, AA763, AB763, AB868, Blackface, Silverface, W/Volume Boost) Tweed Tremolux UPGRADE to Fender part number 125P23D & 041316 nextgenguitars.ca
Output Transformer	Hammond 1760H	$93.99​	Hammond 1760H - Output Transformer UPGRADE - 4/8/16 OHM Added 4/8/16 OHM secondary. nextgenguitars.ca
Choke	Hammond 194A - Choke - 4H, 50mA	$31.99​	Hammond 194A - Choke - 4H, 50mA
Reverb Driver	Hammond 1750A - Output Transformer - 25K, 8 OHM, SE, 3.5W	$46.99​	Hammond 1750A - Output Transformer - 25K, 8 OHM, SE, 3.5W Replacement for Reverb Driver Equivalent to manufacturer part number #125A20B & #022921 nextgenguitars.ca
Cabinet	Veteran Guitars	$400.00​	Veteran Guitar Cabinets (see Facebook)
Tubes	Premium Package	$445.70​	Fender Deluxe Reverb (AA763 and AB763) - Premium Package This is a premium retube kit for Blackface and Silverface Fender Deluxe Reverb (AA763 and AB763) tube amps. Note, this is for the versions AA763 and AB763 using 5AR4 / GZ34 rectifier tube types. www.thetubestore.com
Chassis +	Boards, Doghouse Pan, Faceplates, Footswitch, Knobbies	$450.00​	MOJO - includes $75 shipping
Reverb Tank	MOD 4AB3C1B	$57.00​	Nextgen
Reverb Tank Bag	17"	$20.99​	Nextgen
RCA Jacks		$10.19​	Shielded RCA Cable - Stereo Right Angle (3 feet) Right angle RCA cables for Reverb Tanks and other electronic devices. nextgenguitars.ca
Legend 1258	Eminence (client's choice of speaker)	$166.39​	Eminence 12" Guitar Speakers - Canada Eminence 12" guitar speakers for building or repairing amps and speaker cabinets. nextgenguitars.ca
Components	Passive components and hardware-NextGen	$355.00​	(Pots, jacks, switches, tube sockets, lamp, capacitors, etc.)

A big shout out to the folks at NextGen Guitars! They're a Canadian outfit located in Ottawa (Nepean). Reasonably priced components, outstanding customer service (I think the owner, Jonathan Beals is a GC member). I also have to acknowledge and pass along kudos to Derrick Bell at Veteran Guitar cabs (some of you probably know Derrick) for his great work on the blackface cabs he builds for me. He is kind enough not to chuckle at me when I ask him about my crazy design ideas.

 

So, I'm still having issues with voltage.

I'm seeing B+2 voltage of 490VDC coming out of the doghouse and going to the reverb driver. This is definitely high since the 12AT7 at V3 is expecting to see ~410V. Any ideas why my B+2 is so high?

Incidentally, I've got 490VDC going to the plates in the power tubes (V6 and V7).

I'm at a loss here. Is it possible I have blown 10K resistors? A leaking or open cap? Any ideas?

EDIT: My mains are stupid high (126VAC)..

 

Any ideas why my B+2 is so high?

what's the PN for the power transformer?
I ask because I want to determine the DCV.
Sorry, I did not check your PL above...it does say 291BX?

 

At 126VAC, the 291BX will produce 489VDC, with no load.
126/120 × 330 × 1.414

 

The circuit is an original AB763 circuit?

 

Yes. Yes and yes.

It is almost exactly 489 VDC.

 

Voltage drops: R1 60V and R2 100V.

 

Use Ohm's law to determine: Voltage B - Voltage C / 10,000.
and the same for Voltage C - Voltage D / 10,000.

 

The math is the easy part (at least for me). The problem is that I don't know where exactly to measure Va, Vb and Vc, Vd.

 

Okay, I'll highlight the points on the layout drawing.

 

Hold up. If I am doing this right, my readings are:

A=484V
B= 484V
C=380V
D=315V

Which would provide answers to your questions:

Vb - Vc / 10000 = 0.0104
and
Vc-Vd / 10 000 = 0.0065

And I am sure this must mean something. Hints as to what?

 

I confess that I don't understand why we bother running wires in and out of the doghouse for B+2 since we could pull exactly the same B+2 voltage from the mainboard off of the choke. It seems like a silly exercise to me since it's B+2 no matter where you get it from. Is it to prevent interference on the long run to the V3 and V5 plates?

EDIT: Wife wants me to break for dinner. I didn't even realize it was that time!

 

Is there any functional issues with the amp, presently?