50´s PA amplifier. R.I.M.E.R. / NOVA (Italy)

[chocopower]

Hi there,


I have the possibility to buy this old italian P.A. amplifier with speakers.
I tried to find any information without success.


Any idea will be welcome!


Thanks in advance.

[jjasilli]

Maybe for the right price.  The trannies look to be heavy.  Presumably PT primary matches your wall outlet power.  If the tubes & circuitry are weird, you can gut rebuild with tubes & circuits that match the amp's PS and current rating.

[Ritchie200]

Looks like a re-branded unit, RIMER is probably just the distributer.  Is there any other info inside the chassis?


Jim

[sluckey]

What do you have in mind to do with this amp? Hopefully there will be some info on the chassis or PT or power plug that will give you a clue about what wall voltage it requires.

The speakers are field coil (electro magnets instead of permanent magnets). This will require B+ voltage for the field coils so the power supply will look different than a typical guitar amp power supply. And they will have to be plugged in for the amp to operate. Sometimes there is even a jumper in the connector plugs that will kill the AC mains if not plugged in. The field coils are probably good but the speaker cones are likely rotten and will probably crumble when energized.

I don't see an OT so if it's on the chassis somewhere it's likely kinda small in comparison to the PT.

The tubes inside those metal shields likely have grid caps and may be hard to find.

I would not buy this amp with the idea that it would make a cool looking guitar amp. It will require a lot of work to get it to that point. If I had this amp I would fix what's broken and evaluate it for what it is. Then you'll have a better idea of what it can be. I would not even put power on it until I had drawn a schematic.

Our friend kagliostro  may be able to get you a schematic or more info on the amp.

[eleventeen]

Pretty much agree w/Sluckey, unless you are pondering rebuilding it much like it is; with wimpy speakers and OT, you could really be buying not much more than a power transformer and admittedly coolish-looking chassis and some skungy old parts. I have no idea of whether you consider the existing cabinet arrangement usable.

[kagliostro]

I'll try to find info and schematic


but very very often to have this kind of info about old italian brand is as to be looking for secret aerospace plans of NASA or RKA


Franco

[chocopower]

Hi, thanks for your interest.


The amp work in 220AC like here, in Spain.


In the second picture you can see (i think) more transformers just behind the tubes with metal shields. (in the bigger version of the picture i have, is more evident)


Right now i just have those picture, not the amp.


About the speakers, you said the are "Field coil speakers". My question is if could the O.T. work with modern/usual speakers?


As jjasilli said, my idea was rebuilt it with more common tubes. The price will be about 100€ shipped.


thanks!

[sluckey]

My question is if could the O.T. work with modern/usual speakers?

Absolutely. But you'll have to modify the power supply. Basically just measure the field coil resistance and replace with high wattage resistor(s). You may even want to put a choke in the power supply. At this point it's hard to tell what the amp may be, but I'm guessing it's a simple single ended power amp with a simple preamp for several mic inputs.

[kagliostro]

Chocopower if I was you I put more interest on this


http://www.ebay.it/itm/FBT-MARSHALL-TESTATA-AMPLIFICATORE-VINTAGE-FBT-500R/131355567487?_trksid=p2046732.c100040.m2060&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20140107095009%26meid%3D65dbb13f4c024948a98f3ee607346120%26pid%3D100040%26prg%3D20140107095009%26rk%3D4%26rkt%3D4%26sd%3D281510077395


The original, as the vendor specific, used el503 (very expensive tubes) but he converted the amp to el36


Ciao


Franco

[chocopower]

 nice amp, but boring.,

I like weird amps, guitars, girls..

Now, being serious, i love take those olds 50,s amps, draw the schematic and back them to life after decades sitting in a garage.

[sluckey]

Now, being serious, i love take those olds 50,s amps, draw the schematic and back them to life after decades sitting in a garage.

Post the schematic when you're done. Might inspire a bunch of ideas.

[chocopower]

Amp is here!


Some information:


--TUBES-- 

1x 6J7-6
1x 6A8-G
1x 6Q7-G


1x 6L6-G


1x 5Z3 (Not sure about that)



--TRANSFORMERS-- Manufacturer: NOVA.

POWER: Serie 314 / Mod 8.      85 V.A.


O.T.: Mod 1161.    Primary: 2500 ohms  /  Secondary: 2x 10 ohm speakers (labeled and measured)


CHOKE: Mod 11270.   20H - 312ohm - 75mA.



--SPEAKERS-- Manufacturer: NOVA. Mod 71

2X 10 ohm speakers (labeled and measured)


Field coil resistance: 15k (labeled), 14k5 (measured)


----------------------------------------------------------------------


Can´t work on a schematic until next week, but heaters voltages are modern standard (6,3v for preamp and power tubes, and 5v for rectifier).


Field coil speakers relative low resistance (15k) and the presence of the choke seems to make easy the conversion (correct me if i´m wrong).

[PRR]

That's a very high resistance for a field coil. Looks like it wants 300V at 20mA--- straight B+.

So the amp will run without the field-coils. (In many other amps the FC took <100V but was in series with the power supply, so was essential.)

> 15k (labeled), 14k5 (measured)

Put them on the radiator until you can hardly hold them. I bet it comes up to 15K. (FCs will run pretty warm, copper resistance rises with temperature...)

VERY american tube line-up.

6A8?? That is a heptode, pentagrid converter in the US. Great for radio, unusual in audio. That's the socket I'd like traced. Odds are they strapped most of the excess grids to other electrodes, making a pentode or triode. It is possible this rig came at the end of the Octal era, Octal bottles were glutting the market, but radio-types were most available so the designer used what he had cheap.

6J7 is an excellent pentode, voltage-gain for the mike.

6Q7 is made for radio first-audio, is two diodes (ignore them) and a high-Mu triode, very nearly a half a 12AX7 but a shade lower gain.

Never heard of 6L6. <G>

5Z3 is one of the too-too-many rectifier types which has faded from common use. Obviously if it gives you trouble, check the pin-out and wire for the rectifier used in Champs and Deluxes. 5Z3 is a 5U4 on a 4-pin base. Use it while it works. It may out-live you. Keep your eyes open for a spare-- price $16 in America. If can't replace the tube, replace the socket for a 5U4.

[kagliostro]

Never heard of 6L6. <G>

Nice looking tube



Datasheet & info
http://www.r-type.org/exhib/aaa0107.htm

Franco

[chocopower]

Some pictures!

[chocopower]

+

[chocopower]

In that one you can see some wires coming out from the O.T. and going nowhere. The just are spring-ed. I hope the are more secondaries options.

[chocopower]

That's a very high resistance for a field coil. Looks like it wants 300V at 20mA--- straight B+.

So the amp will run without the field-coils. (In many other amps the FC took <100V but was in series with the power supply, so was essential.)

Why you know the amp can run without the field coils? Just for the resistance? In FC stuff  i´m even more a beginner than in the rest of my amp skills.

6A8?? That is a heptode, pentagrid converter in the US. Great for radio, unusual in audio. That's the socket I'd like traced. Odds are they strapped most of the excess grids to other electrodes, making a pentode or triode. It is possible this rig came at the end of the Octal era, Octal bottles were glutting the market, but radio-types were most available so the designer used what he had cheap.

As soon as possible i´ll draw a schematic.

5Z3 is one of the too-too-many rectifier types which has faded from common use. Obviously if it gives you trouble, check the pin-out and wire for the rectifier used in Champs and Deluxes. 5Z3 is a 5U4 on a 4-pin base. Use it while it works. It may out-live you. Keep your eyes open for a spare-- price $16 in America. If can't replace the tube, replace the socket for a 5U4.

Tube seems in good shape, but i´m a bit afraid in using old tubes, specially the rectifiers and power tubes. Could i test it safety using a current bulb limiter?
Anyway, as you said, they are easy to find at good prices. And it´s a really beautiful bottle!!

[sluckey]

Why you know the amp can run without the field coils? Just for the resistance? In FC stuff  i´m even more a beginner than in the rest of my amp skills.

The 15K resistance says the FC will be wired between B+ and ground, not in series with the B+, functioning as a smoothing choke also. You have two speakers so that's like putting a 7500Ω power resistor between B+ and ground. You can just remove the field coils and the B+ will simply increase due to lighter load.

FC stuff is no mystery. A speaker needs a big magnet to operate. Long time ago big magnets were expensive. So, speakers had an electromagnet mounted on the frame. It functions exactly the same as a permanent magnet. The field coil is just a bunch of turns of wire wrapped around an iron core. When you pass a DC current thru the windings the iron core will become magnetized.

Maybe you built one as a kid. A long insulated wire wrapped around a nail. Connect a battery to each end of the wire. Pick up some paper clips with the nail.

I would test the rectifier simply by plugging it in with no other tubes plugged in. Turn the amp on and look for the filament to glow. Measure the B+. Watch for smoke, listen for unusual sounds, and sniff for unusual smells. Be brave. I bet it will work. Use the bulb limiter if you are nervous.

[chocopower]

 


Thanks!

[PRR]

*I* would:

Use A Lamp Limiter!! Use a 60 Watt lamp, same voltage as your wall and this amplifier's wall-supply rating. (I would not worry too much about 220V versus 240V.)

Remove rectifier. Power up. Check for smoke. Check that the other tubes light-up. This proves the 230V wiring, most of the PT, and the heater wiring are all OK.

*Now* try it with the rectifier. In my experience, this is where the "fun" happens. (You might switch to a 40W lamp for this step.) The rectifier might be shorted. The main filter caps can be so leaky they heat and burst. OTOH the PT HV winding may be rotted open, no high voltage at all.

If no disaster, power-down and Use Clip-Leads to measure the high-voltage (at rectifier cathode). With lamp-limiter it will read low, maybe 200V-- but you hope for "high" voltage not zero or a couple Volts.

Do all this with Volume full-down and preferably with speaker output shorted. (This is a Class A amp, a short is safe, will limit voltage spikes in the OT, and I hate trouble-shooting with nasty noises coming out of the speaker.)

[PRR]

> Why you know the amp can run without the field coils?

What Sluckey said.

We know "from experience" (too many years of looking at everything) that the DC power in a field coil is "similar" to the audio watts that the speaker is rated for.(*)

One 6L6 can do 9 Watts (6 to 13 depending). So 4.5 Watts per speaker.

And a 6L6 with 2.5K load will probably be working near 250V 75mA.

4.5 Watts in 15K Ohms is 260 Volts 17mA.

The voltage is a good match.

Two 17mA coils will not pass the 75mA of the 6L6.

So we see the most likely connection is a 250V-300V 110mA high-voltage supply, with 6L6 and FCs in parallel.

And if we remove the FCs, the "under-load" on the high-volt supply is very slight. 110mA, 75mA, probably works the same, just a little more voltage, which the 6L6 can stand.

This is different from the typical radio. They ran a 350V raw high-voltage, dropped 100V in the FC wired series with the output tube run at 250V. If you remove the FC, no power gets to the rest of the radio. So a speaker replacement also means doing something to replace the filtering and dropping action of the series field-coil.

The third way to power a FC is with a separate DC supply. This is how they did it in movie theaters. The speaker was on stage, the amplifiers were far back and up in the projector booth. Long wires to carry the DC from booth to stage were more expensive than a DC power supply next to the speaker, plugged-in on the stage or screen-wall.

(*)There is no "magic reason" for this. The DC power in a FC is all about copper loss. We could reduce the loss with a larger wire size. But that makes the coil larger, increasing the average length of turn, so for the same turns we need a longer length of wire, and more resistance. The loss does fall as coil size increases, but not quickly; meanwhile copper is expensive. Also the larger coil means a larger iron structure which leaks more magnetisim, so we need even more turns.

I have a feeling that FC DC power runs 0.5 to 2 times the speaker rated audio power. Less FC power is lower midrange efficiency but also lower cost. Mass-produced table radios went this way. A PA amplifier needs maximum output, FC power is about as good as final-tube power, so they tended to use higher FC power. In a large movie-theater with 1930s tubes, efficiency was more precious than copper wire, so very high FC powers were used.

[scstill]

6A8?? That is a heptode, pentagrid converter in the US. Great for radio, unusual in audio. That's the socket I'd like traced. Odds are they strapped most of the excess grids to other electrodes, making a pentode or triode. It is possible this rig came at the end of the Octal era, Octal bottles were glutting the market, but radio-types were most available so the designer used what he had cheap.

As soon as possible i´ll draw a schematic.

did you ever draw the schematic of the 6A8 socket. I have a project that might benefit from this Thanks