Recent content by thornev

Thanks for chiming in. Larry. Good to "see" you again. Went to doc today and I came down with Flu B. It's the milder form of flu and should be easing up by this weekend. I've been sleeping almost all day long. I'll get back on this as soon as I'm 100%.

I've come down with some debilitating illness yesterday. Recovering today. Slept for almost 24 hours ! Not COVID thank goodness. Selector switch was always on FM AUTO. I'll try your suggestion. Thanks, grind. Connect a different amp... Are you suggesting that doing that takes the 500-C amp out...

I found a cold solder joint at the junction of one of the "+" leads on one of the 1000uF 'lytics. It actually came apart just by nudging it. I removed the old solder and resoldered, but unfortunately that isn't the cause. Voltage measurements with tubes out hasn't changed.

@grindfix With tubes out, variac @ 115vac: EFB D3 was stable @ -44.5 vdc EFB D4 was stable @ -32.9 vdc Steve's schematic displays -56.2 volts at the junction of D3 and D4. I don't know what these lower voltage measurements indicate other than the obvious "something's wrong." I wouldn't want to...

BTW @grindfix ... here's a good picture of that resistor you thought was causing the issue. I'll see what I can do about accesing D3 and D4.

With tubes out, variac @ 115vac, measured after all voltages remain stable: V8p1 = 334vdc V8p2 = 2.88vac (heater) V8p3 = 387vdc (plate) V8p4 = 334vdc V8p5 = 0.33 mVdc V8p6 = -16.8vdc V8p7 = 2.94vac (heater) V8p8 = 334vdc And for good measure: EFB in = -20.2vdc (from twin 1000uF) EFB out =...

@grindfix Here's what I said in post 36: "@grindfix If it were true that I knocked something out of place or whatever, wouldn't I get the same symptoms with the tubes out? With the tubes out, all the voltages are normal and stable." I'm not sure if you were asking for all pin voltage...

@RS Steve I would agree with you that the EFB is blown except for the fact that I get normal voltages going into and out of the EFB, with tubes out and with tubes in. @gadget73 Your statement about measuring voltages going in and out of the EFB and IBAM boards... It looks to me that it would...

I measured voltages at the output tubes. Here's what I measured at the point at which the voltages start decreasing. Variac is at 115vac, all tubes in. V8p1 = 309vdc (note that I did the mod where I joined all pin 1s with a "bar" and the 100 ohm resistor joins pins 1 and 4 and pin 4 is joined...

@RS Steve Yeah, it looks like you sure did gut that 500-C power supply area. That stupid antenna wire takes up too much space in mine. I don't see the twin 1000uF's in the bottom picture. The EFB board was working fine for months. If it is indeed trashed again, I can't imagine what could have...

@grindfix I do get negative voltage at all pin 6s. with tubes in, they reach -17 and then drop with all other voltages. I'll check that resistor on the EFB, but I'm confident the legs do not touch. I know it looks that way because it's a 2 dimensional view. I'll check to make sure they're not...

I'm pretty good at documenting and photographing the work I'm about to do so I'm confident about my wiring in this case. I did have that one possible question, but even if it were wrong, I don't believe it would be the cause of my voltage drop. I'm starting to believe that the EFB card went...

@jvstratman Thanks for the sug. Tried it - no change. I reviewed my PCB wiring and the only one that's questionable is the treble side pin 4. I can't tell from the pictures I took if that pin is supposed to connect to the treble pot, rear gang or front gang, middle terminal. I believe it is...

Well, it's not the tubes because with the Sylvanias inserted, I still get the voltage drop. Given that the symptoms are the same as when I had to replace something on the EFB board (I'll have to check my notes to see what it was, the chip or I know I had to replace a resistor), I wouldn't be...

@grindfix If it were true that I knocked something out of place or whatever, wouldn't I get the same symptoms with the tubes out? With the tubes out, all the voltages are normal and stable. @eiraved I have a new set of 7591 TungSol tubes. I forgot about that. Thanks for reminding me. Definitely...