B side voltage readings and LED

S

sfojws

New member
I'm having difficulty with the B side voltage readings, and the LED connecting B3 and the center terminal. I've replaced that LED, being certain of polarity. It does not glow, even in the dark (powering up a troublesome circuit and then turning off the light was a true hold-your-breath experience!). Aberrant voltage readings are as follows, with expected readings in parentheses:

17: 154 V (0)
18: 152 V (70-90)
19: 152 V (70-90)
20: 152 V (70-90)
21: 70 mV (0)
23: +/- 30 mv (0)
26: 153 V (70-90)
27: +/- 20 mV (0)
28: 132 mV (0)

I've reflowed and desoldered all of the connections on that side of the circuit, and looked closely (with magnifying lens) for miswiring. There was one correction that I needed to make, i.e. clipping the lead of the 10.7K resistor (1072F) at terminal 20L, which had been in contact with the chassis. All voltage readings above were taken after the excess lead was removed.

I am concerned that I may have overheated one of the components, with the desoldering/resoldering activity. Other than that, I am at loggerheads regarding what I have not corrected. Any thoughts? Many thanks.
 
An LED glowing can mean a whole host of different things, only one of which is that the LED itself is the problem.

Terminal 17 is connected to the chassis, you can't have 154V there.

I would suggest posting some build photos.

All of the Reductions I have ever had in for repair had major soldering issues that were nearly always loose grounding wires around the 9 pin sockets. 
 
Thanks for the reply, Paul. I'll be able to double-check the reading on 17 a bit later. I'll look to post some photos. That may take a few attempts.

JS
 
Greetings - I rechecked the voltage readings today. The reading at 17 was 0, as you reminded me, is expected. All of the other aberrant readings were very close, or the same. A number of readings that are expected to be zero did indicate a trickle of current. I looked again, to ascertain that there was no unexpected contact with the chassis. I reflowed the solder connections of the ground wire at or near the tube socket, and viewed all with a magnifying lens. All were secure when checked, attempting to wiggle the wire loose with pliers. In fact, the connections were secure enough to lift the chassis a millimeter or two from the base. I also checked the connections to the transformer, and all matched the instructions for the 118 V mains voltage.

It's particularly puzzling that there was a small trickle of electricity at a few terminals where a zero reading was expected. Doesn't this suggest unwanted contact? Or, could this be discharge of capacitors?

I'm also puzzled by the consistent readings of ~152 volts when expected readings were 70-90 volts.

At any rate, if anyone can shed further light on the situation, I certainly appreciate your feedback. 

JS
 
Oh yes, I've tried a number of times to post photos, even using a different computer, with no luck. Is there another method that might work?

JS
 
sfojws said:
It's particularly puzzling that there was a small trickle of electricity at a few terminals where a zero reading was expected. Doesn't this suggest unwanted contact? Or, could this be discharge of capacitors?
Click to expand...
This is not abnormal.
sfojws said:
I'm also puzzled by the consistent readings of ~152 volts when expected readings were 70-90 volts.
Click to expand...
152 where you expect 70-90 means something is preventing conduction of the 6922. Are the tubes glowing?

If you're getting an error posting the images, they may be too large for the forum, so try shrinking them by maybe 50%.  Don't shrink them too much though.
 
I'm still trying to send photos. I sense that the problem is not the file size, but that the Photos program on my computer does not play well with others. I've had similar problems since updating the operating system a year or so ago.
 
This morning, I ascertained that both tubes were glowing, both with the chassis right-side-up, and down. I tested the voltages at 18, 19, and 20, with the same results as previously. Are there any other readings that I could take, perhaps with the (red) meter lead connected to the leads on the underside of the tube socket, that would shed light on whether, and where, the tube is being bypassed? Also, is there a way to transmit a photo or two, by some means other than the forum? I've tried numerous methods to find a "back door" method that uploads photos to the forum, all without success. Thank you for hanging in there with me on this recalcitrant situation. 
 
The readings were:

3: 0.87 V
8: 1.6 V

I checked both twice, to be as certain as possible that the alligator clip on the meter lead was not contacting anything other than the socket leads.
 
While out for a head-clearing walk, it occurred to me that you asked for the readings at the sockets (plural). The A socket readings at 3 & 8 were 1.6 V at each.
 
From these photos it looks like a lot of the solder joints in this amp don't have enough solder.  It also looks like a few leads are poking out where they shouldn't be.  Specifically on one 9 pin socket I see a lead poking out of pin 5.  If that lead contacted the center post, it would do a lot of damage to the amp.


The 220 ohm resistor that goes to pin 1 on the B side isn't wired to the correct terminal, and that's why you aren't getting the correct voltages on that side of the amp.
 
Hi Paul - Wow, what a difference it makes to have a second pair of eyeballs looking over the photos! After-routing the resistor in question, and reflowing & augmenting the solder joints, the voltage readings are (almost) all as expected.

The only discrepancy is at terminals 44 & 45, where the readings have been 76 volts, rather than zero. It appears that other builders have encountered this, and your advice has been to run the preamp for 50 hours, to allow the tubes to burn in. Am I reading this correctly?

It will be a few days before the interconnects, to connect the Reduction to the Moreplay, arrive, so I won't be in any hurry to put this to the test. Nevertheless, it will be great to get the Bottlehead components connected to the Hafler power amp that I assembled in 1985 (and the 1980 vintage Linn LP12 that I've rehabilitated). At some time, I'll also be curious to place (temporarily) the Crack into this setup. 

A thousand thanks for your assistance getting things into order.
 
I just completed my reduction build and have ~60 Volts at terminal 44 and 45 but all other voltages check out.  How was this resolved?
 
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