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Another Eico ST 70 thread

Ok I dbted and stuck some tubes in, once I saw the voltages dropped, full line and it was near right. For your sake Jay (btw thanks for stopping by, I'm sure there are resistors before the plate) if anyone wants the hifi engine, sams, or eico build manual pm me and i'll get them to you somehow. Anyway this is what I ended up (after tweaking which I showed) with and the voltages shown from stock.
I'll check for comments if nobody has any objections i'll try biasing tomorrow, if no issues put some music through it
 

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NJ -- You will do better to leave the 2.2K resistor in the circuit. It supplies significant filtering for the early stages which otherwise might allow some power supply hum to creep in without it.

Dave
 
Thanks Dave, i'all put the 2.2k back. .Anybody have an idea why my (S) and (T) are starting so much lower? I suspect line in is a factor. I take it these are all workable voltages now?
 
ok resistor back in. new meter final voltage #s
AC in 113.6 vac
S 445 VDC
T 391 VDC
U 358 VDC
V 226 VDC
W 190 VDC
Y 252 VDC
Z 145 VDC
I'm inclined to think i'm good to go.
 
Actually tweaked resistors slightly and got very close to factory spec. Did balance and bias. Can't seem to get bias on either channel to .38 , both around .22 max. I'm open to suggestions, but i'm going to try and run some audio through it. Here goes nothing.
 
Also minor voltage issue, rechecked dc filament circuit with new meter with 3.3 ohm resistor , I=I'm showing about 10.9 volts. I tried jumping it with a wire . went to 12.4 v. That seems like a more reasonable number. I don't think it should have a bearing on the bias voltage. I'm not sure about that. Rechecked everything (voltages) found with new meter negative dc running low, Shunted 68ks with 120ks which got me to -21.4 on side -20.5 on other. Tried dc balance and bias. I can balance sides to themselves. Can't get bias up to .38. What gives now?
 
Its Alive! Its Alive ! Its Alive!. For you accomplished techs pardon my outburst. For sake of safety I have 5 jj 12ax7s some old ge 6sn7s and a hodgepodge or good testing but by no means matched Westinghouse 7591s. All things considered and not being able to bias properly it sounds freakin' good at first listen.
 
Good morning guys . I'm riding on commuter train so I don't have any of my info in front of me.
Brief summary, I got all HV voltages on.
I had to jump 68k in bias circuits with 120k to get up to -21 v. I was only reading - 102 off diode(-110v in drwg) (its not one shown(the diode) I couldn't find that one , its a UF4007) so maybe that's my issue. If not I had about -17.7 without shunting. If I understand the balance bias adjustment instructions, you set the 4 pots midway, then balance the two jacks, then bias to .38v. The do other channel. Now (again paperwork not in front of me now) I think balance voltage should be 0v which neither channel ever achieves . Once I balance each side bias (I think before I shunted the 68ks to pots, v was slightly higher). One channel about .17v the other at .16 volts at the highest adjustment. I'm stumped. Ideas?
.
 
I don't think the diode is the problem,You line voltage is 113? What is your filiment voltage? Have you changed the battery in your DMM lately? sometimes they will be off wih a weak battery.
 
Two meters same reading. 117.8 now (line it could've varied time of day). I'm sure I don't completely understand this circuit. If I remember right without tubes I had around -21.6 With tubes it dragged down to -17.7 or so. By shunting the 68ks with 120ks I got back to -21 but the bias voltage actually fell slightly. Apparently something is dragging it down. Bad 7591s? They test and sound very good. Even unable to bias it it sounds very good but obviously something isn't right.
 
I've beem collecting for 30+ years,fleamarket every sunday untill 8 or so years ago,then the auction site pretty much killed it.

What kind of coupling caps are you using for C18 and 19?(to 7591's)
 
.1 orange drops (all the .1 400v became orange drops). Ironically before I took it apart, it also wouldn't bias. I figured it was coupling caps or tubes. Even tubes are different now though not new.
 
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Wife I feeling neglected (never a good thing) I've been spending a lot of time on this past few days. I have to pick it up tomorrow, Thanks for the help. Hope somebody has an epiphany!
 
It looks like all of your ac voltages are right on now,so is your bias still low?

Orange drops are great(not suspect)I've heard some PIO sometimes leak,so I wondered

For the last 2 years I've been thinning the herd,I sold about 70 pieces on the auction site.
 
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Yes with the 68ks could only get to .22 after I shunted 68ks (to try and get back to -21) only .16 highest setting , both channels within a few hundredths of a volt of each other
 
Scott I hate cutting you off, I really wanted and appreciate the help. Thanks again I'll catch you tomorrow. My thinking walking out is that I should go back to the 68ks by themselves. Whatever is the problem is what is dragging the -21 down. Good night Scott. Thanks again
 
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