Looking for info on Vintage Ampeg Radson Magnavox

twhitedc · #1 11-30-2011, 05:47 PM

Hey everyone,
I recently came into an old Ampeg that I've been have issues finding any information on. It was evidently manufactured By Radson in Mexico, for Ampeg who was then owned by Magnavox. Therefore, when I spoke to Ampeg's Tech Support earlier today all the woman could tell me was that it is in fact 70's which is congruent with what I was told. Unfortunately she cold not even find any information on anything related to it. There is a Serial Number but no Model Identification that I can find. The knobs across the front read Master, Treble, Bass, Selection (Tape, Phono, Aux), Volume, Mic 1, Mic 2, Mic 3 from L -> R. On the back I have: 3 quarter inch Mic inputs, a Red Ceramic/reluct switch, Phono input, Aux input, Tape output, 2 quarter inch 16 Ohm outputs and bare speaker wire connections. All of that being said it appears to be all original and the entire housing is metal and the previous owner stated that he had been playing bass through it by running into a Mic input and out of a 1/4 output into a standard cabinet. He also stated that to the best of his knowledge it was some sort of multi-funciton prototype which seems accurate. I have tested it briefly and can state that it does conduct and amplify beautiful clean signal from a passive bass very well when used in the above described manner.

So, here are my immediate questions:

1. Does anyone know anything about this or anything like it given the manufacturer and period?
2. The previous owner stated that it was 100 watts, but I have no reasonable proof of that so any ideas there either?
3. In regards 2 the seemingly parallel 16 Ohm speaker outs is it safe to assume that the amp can safely be run at 8 ohms.... After all 2 parallel outputs at 16 ohms should be 8 ohms... right?
-> If not, Ampeg's tech support made a good point. In order to run at 8 Ohms both jacks may need to be in use. If that is the case how can I figure out which one may be the primary jack, and then supply the other with a dummy load.
4. Is it possible that at some point in the last 40 years someone has had this modified to run at different / more common Ohm level. Is such a thing even possible?

Photos:

http://i1237.photobucket.com/albums/...11126-1726.jpg

i_got_a_mohawk · #2 11-30-2011, 05:55 PM

Sounds like it's a PA amp of some sort?

16 ohms is fairly standard in many applications (for instance, most tube guitar amps!)

Can't help you with anything else, but it looks pretty cool. Nice find!

christw · #3 11-30-2011, 06:01 PM

What are the output tubes and how many of them are there?

Give us some pics of the front and the back panels to where we can read everything. It may help with questions like whether the outputs are parallel or using the second output switches taps or not. Clearly it has taps for a variety of standard PA applications. I'd see it as a PA head (prototype?).

JimmyM · #4 11-30-2011, 06:36 PM

The only info I could find on Radson is about a stereo amplifier. Makes me wonder if this isn't for running a stereo. There's no mention of Radson in the Ampeg book at all that I could find.

twhitedc · #5 11-30-2011, 09:49 PM

I'm going out of town for the weekend tomorrow. Hopefully I'll be able to take it apart to take some pics and count the tubes over lunch or something. I'll try to get them up tomorrow. If not, early next week. Thanks for all the help!

twhitedc · #6 12-01-2011, 07:30 AM

Jonyak · #7 12-01-2011, 07:34 AM

Looks like an old mono PA amp to me. never seen one personaly but it looks awesome.

how does it sound?

twhitedc · #8 12-01-2011, 08:50 AM

So far it sounds amazing, but I haven't played it much b/c I don't have a 16 Ohm cab hanging around and I don't want to plug it into an 8 ohm one until I'm sure it can handle the load... The inputs appear to be bridged so I assume they can run at 8 Ohms (2 paralell 16 ohm loads) without needing a dummy load, but I'm not positive, and until then I don't want to take a chance on damaging anything. Thus: how we got to this point....

MAMMOTHvolume · #9 12-01-2011, 09:17 AM

The outputs are 16ohms only, it's 100watts from a pair of 6550s. If you want to use different impedances you'll have to wire up a speaker cable to the other outputs. Negative goes on common positive on impedence of choice.

Looks alot nicer than your average ampeg and ef86's always sound fat in the preamp!

coreyfyfe · #10 12-01-2011, 09:52 AM

Looks like it may have been a stereo amp, given the phono/radio/aux inputs and switching. On ampeg's MI amps of the time plugging into the "Ext Speaker" would trip the alternate winding so you'd put a dummy plug into the main out and plug a cab into the ext out, but it depends on the amp what that winding is spec'd for*, and I don't think I'd expect that same circuit to hold true for this amp, especially since it's not really an ampeg nor a musical instrument amplifier. Either way, pretty sweet looking amp.

*On amps like the B25 the second winding was for 8 ohms and the outputs were supposed to be for two 16 ohm cabs in parallel, but other amps like the B15 were for two 8 ohm cabs and the outputs were in series so the alternate winding (hope my terminology is right here) was for 16 ohms.

twhitedc · #11 12-01-2011, 10:08 AM

So I feel like the general consensus here is that I'm not going to plug it into anything other than 1 or 2 - 16 Ohm cabs. I'll have to borrow a guitar cab. Also, I'm assuming that all of this information also applies to the bare wire speaker connectors. I have some old Yamaha towers from the 80's that I inherited at home but they too are rated for 8 ohms I believe. Thanks for all the help... any additional information is still more than welcome.

twhitedc · #12 12-01-2011, 04:20 PM

Bump.

coreyfyfe · #13 12-01-2011, 04:34 PM

You could find a 4 ohm 2x10 or 2x15 (or something with two 8 ohm speakers) and rewire it for 16 ohms.

will33 · #14 12-01-2011, 05:18 PM

The screw terminals on the brown strip in back are also for connecting speakers with the bare wire ends. You put the "-" on the "c" and the "+" on the screw who's number matches your impedance load. I have an old rca amp that works the same way. Hard to tell from the pics but inside, there should be wires coming off the output transformer that connect to those screw terminals.

KramerBassFan · #15 12-01-2011, 09:24 PM

"Ceramic Reluct"?

**B-string** · #16 12-01-2011, 09:51 PM

Quote:

Originally Posted by KramerBassFan

"Ceramic Reluct"?

That is to adjust the gain and RIAA equalization curve for the "Phono" input (Turntable that plays big 12" CD's with grooves on them

)

Looks like a school PA unit.

Aquila0507 · #17 12-01-2011, 10:23 PM

Quote:

Originally Posted by will33

The screw terminals on the brown strip in back are also for connecting speakers with the bare wire ends. You put the "-" on the "c" and the "+" on the screw who's number matches your impedance load. I have an old rca amp that works the same way.

I have a weird little PA amp somewhat like this too.

The 1/4 speaker jacks on yours make it interesting. Seems like this amp was for DJaying or maybe music classes for schools as b-string suggested. Cool find.

Aquila0507 · #18 12-01-2011, 10:26 PM

forgot to mention that it does seem like you can go down to 4 ohms.

twhitedc · #19 12-01-2011, 10:26 PM

I have thought about using it to power some yamaha 3 way speakers from the 80's specifically for the purpose of listening to albums... I've also considered putting 2 old Earth 15's that came out of a b-2000 into a 16 ohm cabinet for it. I've even considered making a matching 16 ohm 2x10 to put on top. Either way, it's going to see some use!

twhitedc · #20 12-01-2011, 10:29 PM

I don't really understand how the bare wire terminals can go down to 4 ohms, while the 1/4" jacks seem to be strictly 16 ohms. There's definitely a number of questions here.