Magnavox 8608-10

lawdawg · 2012-03-30 11:27 pm

I'm having a hard time finding a schematic for this amp. Can anyone help me out with an 8608 schematic. I found 2 Russian 6BQ5 tubes from Reflector factory that Sovtek bought out....are these good tubes? Also, should I replace to transformers or do those usually last. Thanks

Eli Duttman · 2012-03-31 1:58 am

Soviet era 6Π14Π-ЕВ (6p14p-ev) stock is fine and the tubes New Sensor (the folks behind Sovtek and other brands) sell as EL84Ms are the current incarnation of the variant, which is a genuine 7189 equivalent. OTOH, tubes without the "EB" are junk.

rmyauck · 2012-03-31 8:48 am

Really nice console! Should sound great when redone!Transformers will last for years unless got moisture in them from poor storage etc. Always have a load (speakers or 12-16 ohm 25W resistors) or you risk the output transformers.

Good luck with that!

Randy

lawdawg · 2012-04-15 4:34 pm

OK, the amp is out & I'm ready to start replacing parts. I found a schematic http://i107.photobucket.com/albums/m285/stickman81/IMG_0250.jpg , and a parts list http://i107.photobucket.com/albums/m285/stickman81/IMG_0251.jpg . I don't show C1, C7&C10, C6 & C9.... Can someone help me out here. The 6BQ5 EL84 tubes will be replaced with JJ's, along with the rectifier tube. Resistors are being checked & replaced as needed. Also a 3 prong power cord will be installed. Here is the underside -

Eli Duttman · 2012-04-15 9:23 pm

The 6BQ5 EL84 tubes will be replaced with JJ's, along with the rectifier tube.

Unfortunately, there's bad news. The latest bunch of JJ EL84s are garbage, as in Jamona Junk.

Be safe and buy Russian 6П14П-ЕВ (6p14p-ev), AKA EL84M, tubes. They are reliable and not bad sounding.

amt · 2012-04-15 10:34 pm

Im currently rebuilding a 86xx and have decided to go with a updated circuit. Seems that many people either update the Magnavox circuit or change it to a RH84. There are many threads on AudioKarma pertaining to the 86xx console amp:

Magnavox 8601 recap help - AudioKarma.org Home Audio Stereo Discussion Forums
Maggie console with 8601-00 chassis - Page 2 - AudioKarma.org Home Audio Stereo Discussion Forums
Magnavox Updated 86-01 - AudioKarma.org Home Audio Stereo Discussion Forums

And here is the schematic Im using, although I already have the original 40/40/20uf caps for the supply so I wouldnt change those values yet.

I have a question though, for those more familiar with vintage tube amps. Ive read that the "death cap" can/shouldnt be removed and that a three wire power cord can/cant be utilized. The chassis is used as the ground plane so whats the best way to wire it up. Ive also seen the cap wired between the AC wires (the 86xx)and switchable to chassis ground instead (guitar amps etc)

amt

Eli Duttman · 2012-04-15 11:36 pm

Stay away from using the chassis for the signal ground. Either a carefully planned bus or a "star", should be used. Connect the signal ground to the chassis at a single point, ideally close to where the safety ground is attached.

lawdawg · 2012-04-18 4:49 pm

Jim McShane is going to hook me up with EL84M's (6P14P-EB actually), and Tesla rectifier....Sovtek 12AX7LPS to rewire for 12V. I started replacing resistors that were out of tolerance. Can someone recommend a place to replace the 4 black caps underneath? Thanks

TheGimp · 2012-04-18 7:00 pm

I'd leave the four black caps in there.

Ceramic disk caps in the signal path replace I would.

lawdawg · 2012-04-18 11:02 pm

Any certain kind of caps? I keep hearing/reading about orange drops-- are those used here?

Eli Duttman · 2012-04-19 1:01 am

716P series Orange Drops are comparatively inexpensive polypropylene film and aluminum foil parts. They are good replacements for electrically leaking OEM waxed paper parts. Soviet surplus K40 paper in oil (PIO) parts are another satisfactory option for the signal path, with a sensible price tag.

By and large, ceramic caps. are a no/no in the signal path. Ceramic caps. definitely have their uses, but not as interstage couplers.

lawdawg · 2012-04-19 12:46 pm

Ok, Thanks Eli....Orange Drops will be used. As far as the re-wiring for the 12AX7 - the only question I see is Pin #3 on the 6V shows no connection, and Pin #9 on the 12V shows Heater Center-tap. Those are the only differences. Is that the same as the other two heater pins?

lawdawg · 2012-04-19 1:33 pm

Ok, found this on AudioKarma - thanks to Roggom.
One more thing, the 6eu7 is 6.3 heaters and the 12ax7 is 12.6 you will be running the new tubes with the filaments in parallel.

Since pin 3 is blank we will start there.

Desolder pin 4 wire and solder it to pin 3

take pin 2 wire and solder in pin 4

take pin 5 wire and solder in pin 2

Make a jumper from pin 4 to pin 5

desolder pin 9 wire and hold it off to the side

take pin 1 wire and solder it to pin 9

desolder pin 6 wire and solder it to pin 1

desolder pin 7 wire and solder to pin 6

desolder pin 8 wire and solder to pin 7

take pin 9 wire ( that was off to the side) and solder to pin 8.

Now you can roll in 12ax7 12at7 5965 etc.

Captn Dave · 2012-04-22 7:08 pm

I'm a big fan of the 6EU7. Magnavox used them in just about all of their tube console amps and so you can find them easily enough. I'd encourage you to save yourself the effort and stay with the 6EU7.

I found enough room on the back to mount 5 way posts and a proper power cord. I used orange drops and was quite satisfied with them. Implementing a star grounding system will reduce hum noticeably. If you need a 6EU7, I can hook you up.

Did you decide to stay with the console or remove it?

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lawdawg · 2012-04-22 8:50 pm

I think what I've decided to go with (for now) is to replace disk caps with Orange Drops, and all resistors out of tolerance. Now that I have found directions for the 12AX7, as long as my 6EU7 works - I'll stay with it. The other tubes will be replaced with EL84M's and a nice rectifier. Power cord ground isn't a sure thing - someone said to tie it into the mounting screw of the transformer. I'll leave it in the console until I can buy another console someone is getting rid of, then use it as a stand alone. My Klipsch Chorus II's are anxiously waiting.

lawdawg · 2012-04-25 8:14 pm

Can anyone help me with running a power switch like Captn Dave's? Which wires in The multi-wire umbilical are power? Thanks

Captn Dave · 2012-04-26 1:11 am

lawdawg said:
Can anyone help me with running a power switch like Captn Dave's? Which wires in The multi-wire umbilical are power? Thanks

It doesn't really matter when you think about it. You are going to install a power cord that ties to the primary of the PT with only the fuse and the switch in series. The wires to that 12 place molex plug will get cut and removed when you do that. Crimp a stacon onto your green power cord wire and put that under the PT nut with a star washer and your all set.

Note that you lack the room for a fuse fixture - you can go with an axial leaded slow blow fuse covered with shrink wrap soldered to the power switch lug. Mine idles at 440 ma so a 3/4 or 1 amp fuse should be a good choice. You must have this to protect your PT from tube failures and other accidents. It's surprising but Magnavox didn't fuse their consoles; consequently, fried PTs are somewhat common.

lawdawg · 2012-04-26 2:30 am

Thanks Captn Dave for the insight..... I just worked out picking this up over the weekend. Now I can leave my console as-is.....& have a stand alone.

Captn Dave · 2012-04-27 12:53 am

Which chassis does that one have?

TheGimp · 2012-04-27 3:16 am

Best to use a screw and nut just for the ground. This prevents one from accidentally disconnecting it.

Here is a good explanation on grounding and wiring a three conductor power cable.

Earthing (Grounding) Your Hi-Fi - Tricks and Techniques

Magnavox 8608-10

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