Rebuilding a 7070 and 8080db

Arden

New Member
Members,

I have a working 7070 which has developed a dead channel output problem when the unit is turned on. The problem goes away when you turn up the volume. I assume this will only get worse. Overall it seems to be in good shape.

I also own a 8080db in very good shape on the outside but has smoked parts on the driver and power supply boards. It seems to to make more sense to rebuild the unit replacing all electrolytic caps, opamp, and aging transisitors, than to fix the problem.


1) When rebuilding these units should I have the CERAMIC CAPS replaced with a quality film cap as well???

2) Would ceramic cap replacement be a good idea in the tuner section???

3) Should the rectifiers be replace with modern types???

3) Are they any other upgrades to consider when I have this work priced out by a good tech???
 
Originally posted by Arden
Members,

I have a working 7070 which has developed a dead channel output problem when the unit is turned on. The problem goes away when you turn up the volume. I assume this will only get worse. Overall it seems to be in good shape.
Dirty output relay...pretty common. Could be dirty switches too, but the relay is most likely the deal here.
I also own a 8080db in very good shape on the outside but has smoked parts on the driver and power supply boards. It seems to to make more sense to rebuild the unit replacing all electrolytic caps, opamp, and aging transisitors, than to fix the problem.

1) When rebuilding these units should I have the CERAMIC CAPS replaced with a quality film cap as well???
Leave the stock ceramic's alone. Trust me on this. ...and there's nothing wrong with old transistors...if they test good, leave 'em in. The opamps are BA312 SIP package (Single Inline), and run off of a single supply. I have modded a couple of 7070's and 9090's with modern opamps, but it required building a split zener supply to power the new opamps, as well as an adapter board for the opamps themselves. It's not a rookie job...but it can be done.
2) Would ceramic cap replacement be a good idea in the tuner section???
See previous answer RE: caps.
Should the rectifiers be replace with modern types???
Nothing to gain by doing so, and the style of the stock rectifiers makes it difficult. Skip this.

3) Are they any other upgrades to consider when I have this work priced out by a good tech???
Replace the stock bias and offset pots with 25-turn Bourns trimpots.

Welcome to the site! Glad to have you aboard...:D
 
EchoWars,


Thank you for the informative reply. The work you described overloads my technical ability. I plan to address the receivers late spring/early summer when we finish our den/kitchen remodeling projects.

Iwill contact you directly at a latter date.
 
The stock opamps are not horrid, they are just totally eclipsed by modern offerings. The guys I've changed them for did so pretty much because they could, and it does result in a nice improvement.

The biggest gains are to junk the original electrolytics with Panasonic FC caps, and replace the signal path caps with BlackGate N or NX caps, and replacing the offset and bias pots to something stable (the originals suck badly).

Jump in here anytime...there's always room for one more...:thmbsp:
 
Re: Re: Rebuilding a 7070 and 8080db

Originally posted by EchoWars
Replace the stock bias and offset pots with 25-turn Bourns trimpots.


Echo, I was searching the bourns website and wondering which of the 25 turn pots you use. There are several differint models listed in the range needed on the X0X0 series receivers.

Thanks
 
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