Bogen J330 Revival

[flintstone mop]

Hi All
I KNOW this is not an audio forum, but can I toot my horn for an old friend???

I have had this Bogen J330 amp for a looong time. 6L6 finals. Audio quality was ok. Tone controls were broad and didn't mean much, but I was happy with it.
It was time to look into the broad adjustment of the bass and treble controls and do a capacitor change-out. Crackling sounds every now and then..
Replaced the usual coupling caps and power supply caps. The cathode resistors for the 6L6's were way out in left field.
Replaced the 6L6's and dug into a really crappy design of the tone control. Got scheezo from ePay.
So I looks on the google for tone controls for tube circuits and saw many flavors.
I picked the Baxandall...............    http://amps.zugster.net/articles/tone-stacks
and copied that circuit into the Bogen.

And I did a Timtron and changed a really high value cap in a pre-amp cathode (6SF6) from .033mf to a 50mf electrolytic.

MY GAWD!!!!!!!  I have never heard this amplifier/P.A. reproduce low end or high end like this!!!!!!! It was like being 'born again'.....Typical wonderful tube sound.
I use this amp as the monitor amp for anything that is called radio. The Flex, R390A diode load, etc etc. It drives a Radio Shack bookshelf speaker with a 12 inch woofer and midrange. The tweeter died a long time ago.


Fred

[Opcom]

Many of the older amps were somewhat restricted in bass to work well with the speakers of the time. A word of caution when recapping; don't go too far up in coupling cap values or whenever the stage clips hard, the radical change in average plate voltage will be passed on as a sag and then boost of the DC on the other end of the capacitor. It lengthens the overload recovery time.

[KX5JT]

Hey Fred, I love that link with those circuits.... almost as easy as paint by numbers!  Kudos for breathing new and BETTER life into the Bogen!

[flintstone mop]

Many of the older amps were somewhat restricted in bass to work well with the speakers of the time. A word of caution when recapping; don't go too far up in coupling cap values or whenever the stage clips hard, the radical change in average plate voltage will be passed on as a sag and then boost of the DC on the other end of the capacitor. It lengthens the overload recovery time.

I think you are on to something here  Patrick..........The extra bass and treble I found would have been hell in the days of this amp for feedback. IN THOSE DAYS they did not have anti-feedback eliminators and 32 band EQ then.
What was engineered was more of a pleasant P.A. audio.

Maybe Paul VJB is thinking how many output transformers he has taken out of BLOGEN amplifiers and used for direct grid drive for a modulator???
I'm guilty tooo!
Fred

[WA3VJB]

Hey Fred, I think I've got a 330 kicking around here somewhere.
Isn't that the one with the fake speaker grill and a nice leather handle on one end of the cabinet ?
(no just did a Google, the 330 is much older)

Actually, I've only dismantled one or two speech amps for their output transformers.  

One had an Acrosound with tertiary winding in it that went into the T-368 about 20 years ago, and you remember how THAT made the 4-125A's sing.  The other was out of a little 10W Eico speech amp with a pair of 6BQ5/EL84 in the output, that I used for the 32V2, trying to replicate what Moe, WA3MKS was doing at the time.  Discontinued that lash-up in favor of changing the coupling and bypass caps to different values and keeping all the circuitry inside the transmitter cabinet.

http://www.the-planet.org/dynaco/Misc/acrosound.pdf