1A/1B reading 100v [resolved]

[Brooklynbottle]

Just completed my Eros 2 build and ran through the resistance and voltage checks. Everything within spec except for 1A & 1B reading 100v.
I read through the forum and noted Paul's advice to look more closely at the regulator board (near Au7) and took the following readings:
OA/B 220v
AKREG 7.09
BKREG 7.06
A/B bregs 0
I examined my wiring and solders all look to be up to snuff.
Obviously something is up w/ the BREG voltage.
Many thanks in advance for guidance.
Addendum:
Is it possible that I fried my 431's? I accidentally installed the 220 ohm instead of the 220k ohm and powered up as recommended before I spotted the error and replaced w/ the correct resistor.

 

[Brooklynbottle]

Here are the images of the board/Au7 socket in question.

 

[Brooklynbottle]

One last symptom to report. My EF 86's were warm, but not glowing (when viewed in a dark room).

 

[Paul Birkeland]

Just completed my Eros 2 build and ran through the resistance and voltage checks. Everything within spec except for 1A & 1B reading 100v.

Is this IA and IB on the regulator board over the D socket or on the PC board up front?

OA/B 220v
AKREG 7.09
BKREG 7.06
A/B bregs 0
I accidentally installed the 220 ohm instead of the 220k ohm and powered up as recommended before I spotted the error and replaced w/ the correct resistor.

I'm super confused here.  The manual says to test the board above the D socket and not to proceed if those voltage checks don't pass, but you say you've completed the build so they must have passed at some point?

On the D socket PC board, OA/OB each connect to the breg pads with wire and allow the regulator to work to pull down the incoming B+ to 220V regulated.  You have an appropriate set of Kreg voltages and correct OA/OB voltages, so my suspicion would be that you should redo your Breg measurements.

 

[Brooklynbottle]

Oh boy.
The reason you're confused is because I'm confused more!
I was checking
A1 and B1 at the A & B sockets! (Not on the board).
Everything checks out to spec as per the manual.
The only thing that's a bit odd is IA & IB read 259.8V (on two different meters).
Is this a cause for concern?
Thanks for the assist.

 

[Paul Birkeland]

The only thing that's a bit odd is IA & IB read 259.8V (on two different meters).

On the front board or the board above the D socket?

 

[Brooklynbottle]

The board above the d socket.

 

[Brooklynbottle]

Front board reads within spec for voltage

 

[Paul Birkeland]

My suspicion is that you just have AC powerline voltage that's slightly below nominal, but 5V of difference there isn't anything to stress over.

 

[Brooklynbottle]

Got it. I'll connect the Eros and see how it goes!
Thanks much. Will report the results.

 

[Brooklynbottle]

So close!
My left channel is maybe 20% lower in level than the right.
Here are my readings:
1a 221.1
1b 219.5
OA 166
OB 163.3
OC 95.5
OD 96.6
OKa 96.6
OKb 97.5
OKc 1.53
OKd 1.32

Breg b 221
Kreg b 7.11
Breg a 219
Kreg a 7.11

Seems everything is within spec. Both sides of the Au7 are glowing.
Any ideas?
Thanks again!!!

 

[Brooklynbottle]

PS swapped cables with R channel remaining the same.

 

[Paul Birkeland]

I would let the Eros cook overnight to see if that changes anything.  If nothing changes, also try swapping the EF86s to see if the low level follows a tube.

 

[Brooklynbottle]

Tube swap early on did not affect signal variation. However I suspect suspect "settling in" might be the key. Signal improved a bit with longer play. Thanks again! Will report results.

 

[Brooklynbottle]

The proverbial rabbit hole!
Conducted the following diagnostics:
Dropped to one interconnect to a/b compare Left & Right Eros OP channels.
Hooked up my old Mojo phono pre-amp to r/o channel imbalance from the phono cartridge (was OK)
Swapped a/b position tubes
Finally installed a rudimentary dB meter app which indicated an approximate 10dB deficit in the R channel. Confirming what I'm experiencing.
Seems the Fidelity is fine right channel just quieter.
Any ideas?
Thank you.

 

[Paul Birkeland]

I would be sure that the 10,000uF caps up front and the 100uF caps on the front PC board are well soldered, as a loose joint on one of those will leave you with perfect DC voltages but a large difference in gain.

 

[Brooklynbottle]

Thank you.
I can't imagine what it must be like diagnosing the myriad difficulties created by an army of amateur assemblers of the Bottlehead line of products!
I'll fire up the iron.

 

[Brooklynbottle]

I hate our diagnostic session has hit the second page.
I re-flowed the 100uF caps and removed, swapped sides and re-soldered the 10,000uF caps. No improvement on the R side gain.
Full fidelity, just an annoying deficit in comparative volume.
Any other suspicions?

 

[Brooklynbottle]

Reading through @caderette, perhaps my 6922 is the source the channel imbalance? Switching the 86's didn't change the discrepancy.

 

[Paul Joppa]

Ten dB is about 70% less voltage, not 20%. The gain of the two triodes in a 6922 might possibly vary by as much as 20%, but not 70%!

I see two choices - either gather more data (measure gain at  several frequencies), or just try refreshing all the solder joints. Personally I'd start with those on the eq network tag strip.