Magnavox 6v6 Stereo Console amp rebuild

[santucci218]

Hey guys. I recently picked up a nice old Magnavox 8802. Well, I think it is an 8802, but when I google 8802, mine seems different from most I come across.

I have two 12ax7's, a 7025 for Phono, four 6v6's, and a 5u4gb rectifier. 4 trannies, so I have the choke.

I want to get started recapping and refurbishing this amp. I know a lot of people have done this project before, so I wanted to get some information squared away before I start.

First off, I need to recap the entire unit. Is there any specific brand caps that you guys love? I'm more knowledgeable about guitar tube amps specifically than I am about home stereo.

Also I know there are many mods that can be performed, but it's hard to tell which are actually worth it. I'm not trying to replace transformers and make it into something its not. Some people talk of the lack of bass in this unit. Is there anything that can be done to address this? Obviously a recap will help. I assume I should change both the electrolytic and cermaics, yeah? All the old ceramics I see in guitar amps suck bass when they get old.

I have seen people get metal plates and such for the top of the chassis to give it a cleaner look. Is this something people are custom making, or is there some dealer for these parts around that I can not find?

Any information would be helpful to get started. Thank you.

 

[macyjrm]

We're gonna need to see a photo of your amp to determine what you have. Doesn't sound like an 8802. Mine uses 6eU7s for pre-driver tubes and has three transformers. To plug up the spare holes in the chassis for cosmetic sakes, I used metal tape found at an auto parts store. I cut tape pieces to size and then applied the tape to the underside of the chassis. Then I painted the exterior with a hammered finish spray paint. Turned out nicely.

 

[cademan]

The 8802 uses the 6CA4 rectifier tube and the 6EU7 preamp tubes.

With the 7025 tube, it sounds like you have a model AMP185.

It might be rubbed off but they usually stamp it somewhere on the chassis in bold black letters AMP 185

 

[santucci218]

Hey, you guys are right, its a Amp 185, which apparently is to be restored to a Amp 175 to ditch the phono. I found a thread of some dude, Gordan W, who reccomends the following..

"You can "upgrade" to an .022uf cap, if desired... IME, it works fine, and seems to help make the bass more "linear" (ie "smoother"), to a lower cutoff bottom-end frequency. Especially if you upgrade the other coupling caps proportionally (if it's .047uf, use a .068 or .1, for example) in the circuit. The exceptions are the compensation caps (the tiny ceramic caps to ground)... definitely LEAVE them the SAME VALUE, in order to preserve stability in the amp...I also replaced the 20uf caps (on the cathodes of the 12AX7 first stage) with 20uf (or 2 10uf caps in parallel) 100 or 150 volt mylar or poly caps. Does seem to make it sound a little better..."



Anyways, has anybody heard a finished one of these? What am I expecting volume wise here? I generally run a Carver AVR100 into some Pioneer HPM100's. Would this have the juice to push my HPM's, or should I think about a smaller set of speakers to accompany this when I finish it.

 

[gadget73]

Power output you can legitimately expect around 10 watts. How that will do with your speakers iunno. Outputs on these are 4 ohm though, it will make less power if mated to an 8 ohm speaker.

 

[santucci218]

Are there any bookshelf speakers that are 4 ohm that people dig?

Also still curious about cap brands, and peoples opinions on changing the values of the cathode and coupling caps.

 

[santucci218]

Ok Dudes. Made some progress. Got it powered up today. Haven't done anything yet but jump the power to get it started. Ordered all new caps based on the 175 schematic. One question that I can't specifically find an answer for....


What's with all these .01uf ceramics to ground? What is their purpose, and should I be replacing all of them? Does quality matter here or is just to reduce noise?

Also, I'm blown away at the quality of the original tubes in this thing. The 12ax7's are so unbalanced, but sound good. I tried about 20 other preamp tubes and kept going back to the original, for now.

 

[DFWguy]

How did your restoration go? I just got my hands on one and need some ideas on how to restore one for use with a new turntable and the original speakers.

 

[tom3]

Does that unit use a separate speaker cabinet for stereo? As you get into this you'll find the input is kind of an oddball voltage/impedance. Magnetic phono cart is too low, line output voltage is too high, sound ok but lose the bass control for some reason. At least that's what I found with the one I have. Lots and lots of info on those amps and how to modify. Nice simple tube unit too.

 

[GordonW]

Ok Dudes. Made some progress. Got it powered up today. Haven't done anything yet but jump the power to get it started. Ordered all new caps based on the 175 schematic. One question that I can't specifically find an answer for....


What's with all these .01uf ceramics to ground? What is their purpose, and should I be replacing all of them? Does quality matter here or is just to reduce noise?

Also, I'm blown away at the quality of the original tubes in this thing. The 12ax7's are so unbalanced, but sound good. I tried about 20 other preamp tubes and kept going back to the original, for now.

The ceramic caps from the 12AX7 plates to ground (there should be one of these per channel), should be 100 picofarad (a very small value). That's to limit how high in frequency the amp goes at full gain- so that it remains stable and doesn't oscillate at ultra high frequencies. That's why those caps should be left alone, in terms of value- they have a very specific job to do.

If you are going to change them- then something like a mica cap is a good replacement. 100pf is a common value for a mica cap- just make sure they're rated at at least 500v.

Regards
Gordon.

 

[DFWguy]

Does that unit use a separate speaker cabinet for stereo? As you get into this you'll find the input is kind of an oddball voltage/impedance. Magnetic phono cart is too low, line output voltage is too high, sound ok but lose the bass control for some reason. At least that's what I found with the one I have. Lots and lots of info on those amps and how to modify. Nice simple tube unit too.

Yes, and I actually ended up with the separate speaker. Both of these belonged to my grandfather. I’m interested in bringing the “Berkeley” back to life, with a upgraded tt that won’t wreck the vinyl.

 

[tom3]

The Magnavox Collaro changer in the later models with a good stylus is a decent unit, pretty easy on the records as it has a conical stylus and tracks at about 3 - 5 grams. Plenty of them around. No preamp needed with the OE type cart.