[ab0ez]

I picked up this little Bogen K130 (6AV5 30 watt push-pull) for $10, including all the tubes!

Problem #1, besides some extra crappy filter caps that somebody soldered very poorly into the amp, verified. The schematic calls for a 15ohm 5% current monitoring resistor on the cathode of each 6AV5 output tube. Well, the amp has a 15 ohm resistor on one tube and a 21 ohm resistor on the other. That will be corrected with a pair of 10ohm (makes current calculation soooooo much easier!) 1% 5 watt resistors, pronto!

Also very curious, the schematic calls for 245 volts on the screens. The amp has a 6CG7 variable regulated screen supply, so adjustment is easy. The kicker is the 6AV5 is rated at 180 volts on the screens. It's big brother, the 6FW5 (my favorite for the similar Bogen DB130), is rated only at 220 volts on the screens. Granted, the DB130 runs at ~680 volts on the plates whereas the K130 runs at ~570 volts on the plates, but some testing is in order.

The Selenium Bias rectifier (provides ~-48 volts bias to the grids) is also history and will be replaced with a fast/soft recovery diode from Jim McShane. I'll also replace the 50uF filter cap with a 100uf low ESR cap. This has worked very well on my DB130's, so it should work well in this application.

Much more to follow on this project. Now to find a mate for it......

[TheChairGuy]

I'm sure you'll do wonders with it, Jim 

John

[ab0ez]

Oh, I will certainly give it the college try.  The output transformers are smaller than the Bogen DB130, which uses the same output tubes.  This amp is obviously geared more towards PA use.  I will remove the mic amp section and reconfigure it for hi-fi use. 

[ab0ez]

Looking at the chassis, I think I have room to replace the two old 30uF electrolytic filters caps with 30uF run start caps!!

[ab0ez]

Looked at the physical layout of the amp a bit more last night.  By removing the mic amp section of the amp, there is enough physical room to install a low resistance value choke in the power supply.  This is getting interesting!  Still looking for a matching amp to make a pair!

[hmen]

If you can't find another matching amp you can use it for an HT center speaker.

[ab0ez]

Oh I am sure I will find one......might take 5 years, but I'll find one!

[ab0ez]

Been a long time since I updated this post, but life, work and so forth have been taking it's toll.

I have managed to replace the rectifier tube sockets. The goal is to replace all of the sockets. I had a Bogen DB130 that was driving me crazy because the regulated screen voltage kept jumping around, +/- 20 volts or better from where it was set (+210VDC with 6FW5 output tubes) . Replacing all of the components in the regulator circuit did nothing. Replacing that 9-pin socket cured the problem! You could not tell from looking at the socket that there was anything wrong with it. Obviously, the dielectric was breaking down under high voltage.

That amp, and it's mate, got all of their sockets replaced and are now powering my brother's Klipsch Cornwalls. I gave him the amps for his 50th birthday. They are wonderful sounding. You have to get your ear about 6 inches from one of the Cornwalls to hear any hum or noise. Anyway, if at all possible, it is a good idea to replace 50 year old tube sockets.

So back to the K130. The main B+ 30uF filter caps have been replaced under the chassis, but the originals are in place just for looks......for now....

Still looking for a mate for it!

[ab0ez]

I finally found and won a second Bogen K130. I use them to power my rear pair of khorns. The mic amp sections have been removed, tone control circuitry removed, power supply beefed up, 5V4 rectifiers, and 6FW5 tubes placed in the output sockets. They run 600 volts on the plates and an adjustable regulated 240 volts on the screens. They don't sound quite as deep as my Bogen DB130's, but the DB130 OPT is quite a bit bigger.....

All in all, quite a nice pair of amps for, basically, dirt cheap!

Now if I can just figure out how to attach pictures via my Linux computer to this thread......

[ab0ez]

Here is a quote from a friend that I loaned the K130's to.  He had been using a vintage Kenwood 200 or so WPC receiver to drive his Khorns:

"I got to tell ya I can't get enough of this
system...Kathy and I sit up late with the volume low and
some of the tunes are simply mesmerizing. Sade's
"Is it a Crime" WOW! I work late today so I took
the opportunity this morning to take in the Sade video you
gave me...It's great, I couldn't get away. Led
Zepplin's "Whole Lotta Love" is another that
really gets it on. "