Magnavox Flea Power: Getting More Out Of The 8600 Series - A Lot More!

Somewhere in this thread, I thought there was mention of adding a recommended value for a volume pot after the input for this design, but I can't seem to locate it. Can someone point me there?
 
In Dave's Mod, he said to extend the HV CT lead, and ground it directly at the can cap to reduce hum.. I looked at his pic, but it looks like it was grounded to the T strip ground. Did I see it wrong, or does it ground to the can cap ground?
 
Mr Aqua -- In my unit, the HV CT power transformer lead is extended with a length of black wire allowing it to connect directly to one of the can cap's ground terminals. The connection where the transformer wire and the black wire that's used to extend it meet is a soldered twist connection, sealed by a piece of black heat shrink tubing over the connection.

Dave
 
Dave. I see it now.. Thank you very much. In your pics, and illustrations, are the pin outs shown for the stock 6eu7, or 12ax7? I am basically cloning your mod, except I will use the 6eu7. I am coming along very well with this. Those orange drop caps, are these the .1uf coupling caps? One other question, are those blue caps the 300pf in the NFB loop? My mod is basically being performed using your visual pics of wire runs, caps, and resistors. placement, and color schemes, as well as reading your text. I can't read the schematics very well due to vision loss. Its great to get back into this.I want to thank you for your valuable resource. I am scheduled for cataract surgery soon. and will be able to see the schematics better.
 
My bad. I think I figured it out. Looks like Dave's illustration shows all 9 pins are used in the 6eu7. That indicates he has pinned it out for a 12ax7. Right? Also the blue caps are for the Zobel network, and the orange drops are the coupling caps, all of which are .1uf. I will use Russian PIO caps for the coupling, and 225P orange drops for the Zobel. However, I am confused why Dave changed the 1.5K ohm resistor from ground to pin 9 (screen grid) of the 6BQ5 closest to the transformer, to a 820 ohm resistor.
 
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Without going back through every post. I've blown 2 fuses in mine. Never while playing. Either on power on or power off? Am i the only one that's had this issue? Can i safely bump fuse rating (is there any safe leeway?
 
NJ -- Are you using a 1A Slo-Blo fuse? It may be that the magnetizing current of your power transformer is slightly greater, causing the fuse to open. Moving up to 1.5A will not significantly under-protect the amplifier if you want to try that.

Mr Aqua -- The resistor you refer to (1.5K to 820Ω) does not connect to ground, but between the point where the Red output transformer leads connect to, and pin 9 of the closest 6BQ5 tube. This resistor was "changed" as the original value was given in error. When I was developing the design, I did so operating only one channel at a time. In that scenario, the correct value for that resistor would in fact be 1.5K. But in final form, when both channels are operating at the same time, the value should have been nearly halved to the final 820Ω value I corrected it to. The fact that the original schematic then indicated 1.5K was just an error that "got by".

Dave
 
Dave. I see it now. I will be glad to get my cataracts removed. Was I correct in assuming that your pic illustrates a pin out for a 12ax7? When you speak, I listen. Thank you. John
 
Absolutely correct. When I did that project, it was never done with the idea of offering it up on AK for this thread but rather, was a pre-project to duplicate at a later date with a grandson who was showing strong interest in my hobby. I didn't have any spare 6EU7s at the time for the developmental model, but I did have a ton of 12AX7s, so that's the tube that made the cut, and the pin illustration you see.

Dave
 
Thanks Dave,
Not sure if its a factor but I went SS on the rectifier. Maybe faster in rush surge is pushing the fuse.
It was a 1 amp slo blo . I ordered 1.25 and 1.6. I didn't see the 1.5 when I was looking.
Also I'm speculating but it'd go 20 or more cycles without issue so I'm guessing it's right on the edge?
 
Sure sounds like it. The SS rectifiers would definitely change the fuse parameters, supported particularly by the fact that you say the fuse never blows during operation, only at start up.

Dave
 
Absolutely correct. When I did that project, it was never done with the idea of offering it up on AK for this thread but rather, was a pre-project to duplicate at a later date with a grandson who was showing strong interest in my hobby. I didn't have any spare 6EU7s at the time for the developmental model, but I did have a ton of 12AX7s, so that's the tube that made the cut, and the pin illustration you see.

Dave
Great Dave. I will go forth with your clone. I have a Brimer CV4004 that I received for my guitar amp. I wonder how it might perform in this. John.
 
Hello, I'm new to tube amps, although I've been an electronics hobbyist for many years, tubes were always "old school." Now that I'm old, "old school" seems to be cool again. :rockon:

My son, who grew-up on MP3s, iPods and Bluetooth picked up a small tube amp and a turntable - now all he wants is vinyl records, go figure. That got me thinking, could I build/rebuild an old tube amp and be cool too?

I have picked up a Maganvox 8302 6BQ5 SE as my first tube refurbish and was wondering what was the difference between the 8600 and 8300 series of amps. I have looked at the schematics, but aside from some voltage and passive component differences, I'm at a lost. I have searched the internet and it seems Magnavox made several variations on a theme for this class of amp. Will any of the ideas talked about here for the 8600 be applicable to the 8300?

I have read this thread through many times and have learned a lot. Thanks to all the posters who took their time to share knowledge with lesser mortals like me.
 
I'd have to go look but I'm pretty sure there's a similar thread on the 8300s.
IMHO you have to find your own cool:D.
Look inside. It's there:thumbsup:
After rereading your post , if it's SE 6bq5, this is the one you want. Just follow the bouncing ball
 
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I'm actually thinking of doing the OPPOSITE of what Dave did, with the bucking winding- using it in opposite polarity, to BOOST the B+. Yes, I know that will upset the heaters- but a .5 to .68 ohm, 5 watt resistor in series with the heaters, will put those voltages back down in spec, for the cost of about a dollar...

I was just rereading thread.
Gordon if your interested,I ship you the abandoned carcass (original chassis, with sockets and original OPTs)
PM me if you're interested.
 
Thanks nj phoenix. I looked for 8300s, but did not see much, I guess they were not as popular. This 8302 is a phono only, so the PT may be small. I'll take some measurements once I get my light bulb current limiter built. The only experience I have with vacuum tubes was many years ago tuning up a CB radio - someone keyed the mic when I was connecting a 50 ohm dummy load - I swore off tube gear after that enlightening event.:yikes:
 
Thanks nj phoenix. I looked for 8300s, but did not see much, I guess they were not as popular. This 8302 is a phono only, so the PT may be small. I'll take some measurements once I get my light bulb current limiter built. The only experience I have with vacuum tubes was many years ago tuning up a CB radio - someone keyed the mic when I was connecting a 50 ohm dummy load - I swore off tube gear after that enlightening event.:yikes:

I'm not familiar with the 8300.
My best guess is if it's running 2 6bq5s and a 12ax7 or a 6eu7, it likely has the same power transformer. If you can get #s off or take a picture , somebody here could verify. Worst case scenario you pick up a replacement ( one was suggested earlier in the thread) . I tend to think that will be unnecessary
 
Darn! Was going along good. Got to the last pin on the output 9 pin wafer socket, on my maggie 8601-20, then snap. Can I use a 9 pin ceramic socket for a 12ax7? I have an extra one from another project.
 
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AES sell complete tube sockets (i'm pretty sure i sourced mine there). Many other places do as well (tube depot, ebay). Sometimes you can extract a broken position out of a socket and replace from a similar one. The bitch of it (pardon my language) is you'll wait 3-5 days and pay 5-7 bucks shipping on a 3 dollar socket.
You may want to buy a spare. These had a bad reputation as not being great sockets. Then again they lasted 50 years so they must have been ok.
 
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