Radiogram in a gramophone cabinet.

[Spencervs]

hi guys, I have come across what was an old gramophone, the type that are in a massive cabinet, however someone has gutted out the turntable and the inside horn! so its just a cabinet. I also have come across a lot of radio valves that I wish to use. I was thinking about buying this cabinet and putting an electric turntable into the top and making a radio circuit/amplifier so that the cabinet becomes a radiogram... I would like to know what circuit could produce the best results.

I am unskilled in this field but I really feel up to this task... I am confident that I can build a circuit with a clear diagram.

[vinrads]

First of all you need to decide what type of radio you need ie AM ONLY or with FM and if you intend to use it on a regular basis! If you have limited experience in constructing radios, may I suggest that you install a known good radio with a gram input socket? You could restore the radio before fitting and this would give you some experience.

Mick.

[Darren-UK]

Assuming you'll be making the bare chassis upon which to build the circuit, you might be best examining the cabinet first to decide just how big the chassis can be and where the controls, tuning scale and 'speaker(s) will go. From there you can work out if the project will be worthwhile; if it's only possible to fit a pathetically small chassis then the results may make the project a waste of time.

If the cabinet is the type I'm thinking of, they weren't that big and you may not get the results you'd expect when compared to a proper purpose-built radiogram.

Remember, too, that the cabinet will be disfigured to the point where restoration wouldn't be possible.

Those issues aside, given your admitted lack of skills I'd be inclined to follow Mick's advice if you really intend to go ahead with this.

[Ed_Dinning]

Hi, for an amplifier try one of the Mullard circuits from 3W to 20W, all well proven designs.
Plenty of circuits for AM and FM sets, but you might go for a simple TRF if it is your first attempt as the alignment is much simpler. Or try the exotic such as a Synchrodyne, direct conversion set, these give very good accounts of themselves on AM.

Ed

[julie_m]

ZN414 and TDA2006?

As others have suggested, you might do better to start with an old AC ONLY radio (i.e., one with a power transformer -- important for your safety), probably one that is no looker (someone here is bound to have one cheap -- try the wanted section), and graft that into your cabinet. You can feed the audio from a ceramic pick-up cartridge straight in at the top of the volume control even if there is no dedicated "gram" input.

That will at least get you "up and running" fairly quickly, and then you can work on incremental improvements.

[greenstar]

The nicest thing might be to find a horn and mechanical turntable that would fit and restore the thing. I can't imagine that would be easy, but could be one somewhere with a bad cabinet.

Tony.

[Spencervs]

Hmm I am thinking of the Mullard 5-20W amplifier. Could I just make my own and use a copper circuit board, or do I have to use a conventional chassis?

[Spencervs]

also does anyone know what the pre-amp for this is? it mentions that you can have a 2 or 3 valve one with 16,000 K Ohms... is this set up going to be that powerful? I thought 20W was quite low on volume?

[Herald1360]

Not sure what 16,000 K ohms has to do with preamps, it's just another way of saying 16 megohms or 16 million ohms, which is a high value resistor.

20W from a valve amplifier into any speaker set up of the period will blow your head off in an ordinary living room. What it won't do is drive a modern low efficiency HiFi speaker very loud. They're low efficiency because high power solid state amps are cheap and it's easier to design a flat response speaker by flattening all the response peaks down to the level of the most insensitive frequencies than any other way.

FWIW the highly thought of and still seriously desirable Quad II power amplifier is "only" 15W output.

[Spencervs]

ok but what pre-amp will be sufficient? I was reading the diagram on this http://www.r-type.org/static/5-20.htm and it said about a pre-amp being 16 K Ohms and it can be 3 valved or 2 valved... any suggestions on a circuit?

[val33vo]

I know this will sound like sacrilage to the regulars on this forum but why not buy an old valve record player off e-bay and strip the parts out of it, much cheaper than building one yourself ( The transformers cost a fair bit now )

Hacker cavalier or bush SRP31 spring to mind

regards

val33vo

[Baggrus]

If I was building a valve amplifier from scratch these days I would not follow "old school" ideas with all the heavy metalwork. A basic chopper psu or balanced supplies (depending on the output arrangements), followed by a couple of stages of amplification (ECC83's anybody) and an OTL output stage. (couple of PL36's maybe)

Only things I would not use solid state components for would be the active audio path devices.

[llama]

From memory, the 2- and 3-valve pre-amps are from the original Mullard valve circuits book so you'd need to look those up to see if the facilities offered match your requirements.

Note a 5-10 with built in tone controls gives a sensitivity of quoted 600mV which may be just enough for a ceramic cartridge.

I'd be wary about driving 20W (from the 5-20) into a speaker housed in the same cabinet as the turntable. Likely to be way too much acoustic feedback, making the stylus jump out of the groove.

Graham

[G8HQP Dave]

It might be possible to build a 5-10 or 5-20 on a PCB, but two snags:
1. you still have to put the heavy transformers somewhere off the PCB,
2. stability can be a problem unless you follow the Mullard tagstrip layout and wiring exactly (i.e. not just the circuit but also physical placement).
My guess (forgive me if I am wrong) is that you are fairly new to all this so the chance of it coming out right is small.

The Mullard preamps are not suitable for modern high output devices, and may be too noisy for a magnetic cartridge. You are unlikely to find a gramaphone cabinet with anything like enough room for all this anyway. Either include a small circuit, such as the 3-3, or build your amp in another box.

[Herald1360]

Originally Posted by Spencervs

ok but what pre-amp will be sufficient? I was reading the diagram on this http://www.r-type.org/static/5-20.htm and it said about a pre-amp being 16 K Ohms and it can be 3 valved or 2 valved... any suggestions on a circuit?

Gotcha. This little table simply refers to the value of resistor R16 in the decoupling circuit feeding HT out to the preamp. Depending on how many valves in the preamp, the value changes to keep the voltage for the preamp about the same.

The two and three valve preamps themselves will be other Mullard designs probably elsewhere in the same book about amplifier design that the 5-20 circuit and details are in.

The two valve circuit (in stereo form so four valves here) is also in r-type.org at http://www.r-type.org/static/pre.htm

[love kt3]

hi,i sugest you build a mullard 3-3 amplifier,and feed it from a mp3 player. you dont need a pre amplifier.with a good speaker you would get good sound,and 3(real)watts are planty.you can buy a ready made aluminum chassis to fit the space you have.
if it all works out well,then as the second stage get a turn table and pre amplifier.
you could get most of the parts from a junk sixtees ac only radio.