Help me finish my EICO HF-20 rebuild!!!!

[analog addict]

So here's where I started.....

http://audiokarma.org/forums/attachment.php?attachmentid=83149&d=1205768341

along with the original thread (http://www.audiokarma.org/forums/showthread.php?t=133076&highlight=hf-20)

and here's where I am now....

http://photos-e.ak.facebook.com/photos-ak-sf2p/v309/27/44/1316738/n1316738_33632804_1761.jpg

I have the loose caps to replace both of the power supply multi cap cans underneath, but I am not sure of how to wire them in. Here's a close up of the underside....

http://photos-g.ak.facebook.com/photos-ak-snc1/v262/27/44/1316738/n1316738_33633006_4981.jpg

I have 30uF's, 22uF's and 10uF's, all 450 VDC.

Here's what I think I need to do.

The pink arrow points to where 2 of the 20uF caps are wired together, creating the 40uF cap first stage for the 450VDC coming from pin 8 of the 5U4GB, and going to two leads of the OPT, one of which is identifiably red. I'm guessing I lift the connector from the 2 positive terminals of the 20uF sections, and connect them to the positive terminal of a new 39uF cap. then I ground the negative terminal of the new cap to chassis ground. I think I need to get a couple of multi terminal strips from the Shack to anchor the + ends of the new caps. Essentially repeat for all the other stages. Am I barking up the right tree?

If so, I'm still gonna post pix of the final wiring before I fire it up.....

Also, on this amp, there's a 47Kohm resistor from the Treble/on-off switch lead pictured to ground. The other amp has a straight wire in it's place. Which should I use?

http://photos-d.ak.facebook.com/photos-ak-sf2p/v309/27/44/1316738/n1316738_33632803_1451.jpg

Thanks for all the past help and the help yet to come....:thmbsp:

[cademan]

Personally, I would leave the can capacitors alone as long as you had no hum or buzz before the rebuild. It's been so long sinse I rebuilt my magnavox, but it still has the original cans. Just the underboard coupling caps and such have been replaced, along with out of tolerance resistors. Unless I have it written down (which I don't), I refer to www.philsoldradios.org for capacitor values in parallel or series. I can't remember offhand if the 5U4 rectifier doesn't like anything below 20mfd, or 40mfd. If the two 20mfd on the cans are tied together to make 40mfd, then you only need to use one at 40mfd @ 450volts.

[analog addict]

My capacitance meter reads one of the first stages as 65uF, so I know that one has to be changed. And if I change one, might as well change them both. Who knows how long the original cans will last, especially with a fair amount of use.....:dunno:

Besides, I was thinking about beefing up the stages after the 40Uf cap anyway....:scratch2:

[cademan]

I was just curious! You are doing a good job! I'm still using my 50 year old magnavox daily with its original cans.

[willyrover]

My suggestion is to either:

A) Gut the old cans and install the new caps inside them. A Dremel with a cutting disc should be able to slice off the base, remove the guts, solder the new caps inside using heatshrink where necessary , and tuck the whole thing back into the tube.


B) Use a lug strip with the same number of contacts as the original cap +1 for ground. Replace all the resistors in this part of the circuit as well then patch it back in. Leave the original cans in place but completely remove them from the circuit. (see top left corner in pic)

C) Use a small project-board to hold the resistors and capacitors in the circuit and mount it to the amp with short standoffs. (see pic #2)

[analog addict]

My suggestion is to either:

A) Gut the old cans and install the new caps inside them. A Dremel with a cutting disc should be able to slice off the base, remove the guts, solder the new caps inside using heatshrink where necessary , and tuck the whole thing back into the tube.

Essentially...too much time and too many 4 letter words...




B) Use a lug strip with the same number of contacts as the original cap +1 for ground. Replace all the resistors in this part of the circuit as well then patch it back in. Leave the original cans in place but completely remove them from the circuit. (see top left corner in pic)

You read my mind....Keep it point to point at least. Good practice too...:thmbsp:

C) Use a small project-board to hold the resistors and capacitors in the circuit and mount it to the amp with short standoffs. (see pic #2)

Too organized, and too much additional thinking for what's supposed to be recreation. Sheer coincidence that I picked up a 4 pack of 5 connector terminal strips with the center terminal having a lug to ground? I don't think so...:D

http://rsk.imageg.net/graphics/product_images/pRS1C-2265726w345.jpg

I'm not keen on risking the amps to a flip of the switch. I'm gonna post pics for a final opinion before adding electrons.....:yes:

[Elliot Thompson]

I would suggest researching and buying a new Power Transformer. The Eico HF 20 is nortorious of having an extremely Hot Transformer (While just idling)
to the point it will burn your fingers.

That is the only pitfall I remember about owning that model.

Best Regards,

[analog addict]

Still have a remaining issue or two, but up to 100 VAC on the variac, no smoke, no fire, no sparks, no sizzling sounds. IR thermometer measurements of the rectifier tube are within a couple degrees too. Making some nice sounds on some original Wharfedale Diamonds....

http://www.audiokarma.org/forums/attachment.php?attachmentid=110668&d=1222652336

Here's the amateur but apparently functional bypass job. Good thing there's lots of room under here....:thmbsp:
Thanks to HomerJSimpson for checking my wiring job....

http://www.audiokarma.org/forums/attachment.php?attachmentid=110670&d=1222652336

http://www.audiokarma.org/forums/attachment.php?attachmentid=110669&d=1222652336

Now for the remaining bugs....:scratch2:

The recapped amp has much less gain, but clearer highs. Originally when I started the restore, I noticed that the middle (loudness) knob/pot was frozen. Some de-oxit/fader lube got it going again, but I think I am going to have to compare resistance values between the Level and Loudness pots on the amps, and possibly source some replacements.

As for the sound difference, could replacing the PS caps make the high end clearer, or do I need to look for some other issue in the 2nd amp? I ran all the tubes I'm using thru my Hickok 533A to make sure I could rule out tubes as a source of trouble. I may just change all the tubes back and forth to be sure.....:scratch2:

Ideas???

[analog addict]

I would suggest researching and buying a new Power Transformer. The Eico HF 20 is nortorious of having an extremely Hot Transformer (While just idling)
to the point it will burn your fingers.

That is the only pitfall I remember about owning that model.

Best Regards,

The power transformers are only moderately warm to the touch. Could be that yours has PS caps that had drifted?...:scratch2:

Also, I think the high freqs on both amps are equivalent. This amp has a funky on-off switch. It's incorporated into the treble knob, and you have to be careful to turn the treble knob to the same position on each amp.

I smell a power strip in these amp's future....:thmbsp:

[skykng]

Hi AA: I just read this thread about your Eicos--. You have done or are going to do what I would do: leave the cans in place, bend the old terminals down out of the way, wire the replacement caps in permanently to terminal strips and call it a day. I would add some capacitance while I am at it: 39mfd to a 47mfd for example. Good job!! I also agree with replacing the caps now - !Did you see my redo of my Fisher 460A ps/amp - working with Dave in Ct while he does his. Same idea. In the "Tube Audio" - page 3 - "Fisher 480 Cap Questions" 9/25 8:34pm.
#1 priority: is it safe? (neat, clean, run cool, no chance of shorts, good soldering, insulated where it needs it, and physically strong)
On the treble control tap, I would put the 47k in there --- gnd
is usually on the end of the pot (500K is common) through a capacitor. What does the schematic have?? good luck and
congrats! steve

[skykng]

Hi again: I just read your original thread -. I agree with Avionic,Homer, and Soundmotor -- easiest, best way to check a power transformer is to pull the rectifier tube. Now measuring AC voltage (repeat AC voltage) measure the HV winding @ pins 4 and 6 on the rect tube base. This will be noload high voltage, and then measure the filament of the rect tube (maybe 6vac without the tube for a 5v tube) and then check the other filament winding for 6.3vac (maybe 7vac no load). No smoke, stink, blown fuse? Transformer is likely OK. Now you can plug in the tube and check the output at the tube filament - DC voltage -
and high - be cautious - go from there.
best, steve