A Gramophone Amplifier from 'JUNK'.

[Heatercathodeshort]

This is indeed a dangerous path to tread. My thoughts exactly Alex. I have loads of old decks and pick up heads. Might even consider a 'Hybrid' with a clockwork motor. I have some incredible late 20's pick ups that look more like something from a bomb disposal unit!
I'm continuing with this project and so far it is going far too well. I'm just waiting to be tripped up..The case is all but finished but I need to locate a very large nut for the deck as the original is monkey metal and breaking up. Other than that it sounds great. I will post all the results. If this turns out a complete success I may have a go at constructing a repro player from the early days of electric recording. Big strange valves and 'bolt down' components. I have all the bits but life is just too short. John.

[Heatercathodeshort]

The way this has ended up leads me to think that the title should now read ' A 78RPM gramophone from 'Junk'
Well the white coats are definitely on their way. I must be careful when I open the front door to strangers.

I continued with the gramophone project and managed to finish a suitable case. I refuse to call it a cabinet as the quality of carpentry has a lot to be desired. I continued the junk theme and only used timber [Sorry Mr Chippendale] pulled from skips and odd bits of trim left over from other mad projects.The result can only be described as 'serviceable' rather like the dark coloured paint people used to cover their houses with so as not to 'show the dirt'.

As previously mentioned the 1930 BTH pick up required a complete overhaul. The coil was fine but all the damping rubbers had turned to Bakelite. It is quite a work of art with what appears to be a brass case. It must have been very stylish back then.

Now the interesting bit a Simpsons Electric Turntable from 1930....
As can be seen from the pictures it resembles a huge electric clock motor. The base unit contains the mains coil and the turntable underside contains the other half. The turntable sits on a substantial bearing and is very free running. You have to spin the turntable to around 70 RPM to start it and then the 50c/s mains takes over producing exactly 78 RPM with a fair bit a torque.
It is completely silent in operation but does not lend itself to speed control or automatic operation and does not feature an autostop. Fine back in the early electric gramophone era but soon superseded by more conventional changers. A large brass nut from some old plumbing fittings, cut down with the hack saw, has made an excellent replacement for the rubbish metal original. As Charles Hawtrey would have said. 'What fun!'

A final small modification to the amplifier was to fit a Mazda 6P25 in place of the Mullard EL33 originally selected. I find them more robust than the EL33 and only required a change to the bias resistor.

It really does sound great and I'm sure it will create a bit of interest along side my ancient Rogers unit I have used at the shows for many years.

Complete madness! I will never mock your Masteradio again David. [Well at least for a few days] It's been a very long time since I constructed anything on this scale but it has used up all manner of junk and made something of interest out of it. I've also discovered all manner of 'lost' items while searching for woodstain, screws and bits of Paxolin.

Tommy Dorsey never sounded better.. Regards, John.

[Heatercathodeshort]

The final pictures.
The original purple [ughh!] turntable mat was moth eaten and ugly. A new one was cut from an old felt hat and glued using aerosol photoprint glue. The can was about 20 years old but was still up to the job. Yes David, complete madness! [Don't ask where the felt hat came from...] J.
PS. I nearly had a disaster when I shortened the speaker leads. I cut them without thinking and let all the Oxygen in...Luckily my mate works for BOC and with his advice managed to get it all out again saving the day..

[FERNSEH]

Originally Posted by Heatercathodeshort

As Charles Hawtrey would have said. 'What fun!'

Hi John,
Was it not "Tremendous Fun"? He said it in the fight scene from the film Carry on Don't lose You're Head.
Anyway, the cabinet looks great, a real solid job. And that pick-up, that's something else.
I hope this interesting construction project has now inspired others to take up the challenge. As I've written before, every audio enthusiast should construct a Mullard 3-3 amplifier and yours is essentially the same thing. Pentode amplifier and power tetrode or pentode in class A operation.

DFWB.

[Heatercathodeshort]

Yes David, that is how we learned, hacking away at tobacco, baking and biscuit tins to make chassis!
You can use all sorts of transformers and odd valves never intended for the purpose and still get decent results. It's very difficult to destroy the valves unless you drop them of course. This amplifier would be very much at home with a later, lighter pick-up and play 45's and LP's of course.
I've placed the gram in the living room for a few days as I have a visitor tomorrow and I'll need the workbench.
These two pictures are a little worrying. I had no idea I lived in such a time warp. Must drag myself fully into the 20th Century...John.

[Peter.N.]

Very nice job John both the electronics and cabinet. I was usually more concerned with getting the thing working than what it looked like, you have done both, well done.

We had an old radiogram at the shop which was ac/dc, it had a disc type induction motor and a valve inverter driving it, never seen one since.

Peter

[FERNSEH]

Originally Posted by Peter.N.

We had an old radiogram at the shop which was ac/dc, it had a disc type induction motor and a valve inverter driving it, never seen one since.

Made by Ace radio? Employed two 50CD6G power tetrodes to drive the gram motor. I was asked to repair one way back in the seventies, or was it the sixties. It's so long ago now.

DFWB.

[Nickthedentist]

Very nice work indeed, John. I'm impressed with how quickly you got it done too.

What a bit of luck about your mate at BOC!

N.

[m0cemdave]

Originally Posted by Alex728

With the first I read in some old book about a dual turntable unit which had an inbuilt crossfader used in AV installations in the mid 20th century

That's what was known as a "Panatrope". They were used in theatres for playing sound effects cues before tape machines (remember them?) became ubiquitous.

In 1972 my University had one in the main assembly hall, consisting of a pair of Garrard 301's with Metrosound Hi-Jack groove locating units. It dated from around 1965 and would be worth a fortune today.

There's lots of information on old DJ console units etc on another forum:
http://forum.speakerplans.com/golden...s_forum28.html

[Alex728]

Originally Posted by m0cemdave

That's what was known as a "Panatrope"

cheers - I remember reading about those when I was a lad and even then was interested in DJ'ing...

Also found an older version of two grams mounted into this huge rack panel, was from a company called Pamphonics I think. Looked like the sort of PA you would get in a nuclear bunker, maybe the idea was that even if the bomb was dropped you could still have a rave .... actually a retro style DJ setup would be an interesting project for someone, you could start beating the youth at their own game

[Heatercathodeshort]

Stop it Alex. I'm very old and a rave would probably kill me.. Cheers, John.

[Peter.N.]

Originally Posted by FERNSEH

Made by Ace radio? Employed two 50CD6G power tetrodes to drive the gram motor. I was asked to repair one way back in the seventies, or was it the sixties. It's so long ago now

This was in the '50s and it was old then, I think it was a 78rpm only deck, I thought it had British 7 pin valves but maybe not.

Peter

[AC/HL]

Ace RG354U. http://www.service-data.com/section.php/283/1/rg354u
It refers to an Autochanger, but doesn't say which one.

[P.Pilcher]

Delighted to note your careful preservation of oxygen free speaker cable. When I had my classic discussion with the Quad service lab, having just taken delivery of my ELS 63's all those years ago, they assured me that when one of their number went out demonstrating their loudspeakers, they were usually connected to the amp using lawnmower cable! (My 63's still sound beautiful.)

P.P.

[Techman]

Loving this gram!

When I was a teenager, I built a record player from scratch out of junk, for my young niece as either a birthday or Christmas gift - can't remember which. I made the amplifier from scratch including the chassis. Used an old TV speaker and cut a pencil down to make the record spindle. I can't remember where I got the turntable from or why it didn't come with an arm or a spindle, but it had three speeds and I mounted it on a sheet of plywood with a crude plastic pickup arm. I painted the whole thing bright red with that 'Household' brand paint. It had a mains transformer and I fitted a three core mains lead.

When I asked her about it a while back, she said it eventually got chucked out, but it did work very well.

Don't worry about your living room - it looks a bit like mine!

[Heatercathodeshort]

I have done a bit of tweaking with the negative feedback. It was slightly excessive introducing slight distortion when playing near full output and an increase from 10k to 12k of the feedback resistor has cleaned things up. It is now very sharp and gives a good account of itself in the open air.
I have also replaced the rather soft top damping on the pick up [fitted earlier] with a slightly firmer rubber. This has again improved quality to just about as good as it gets. I have played some heavily modulated recordings and the pick up appears to cope very well with soft tone needles and no noticeable wear to the shellac recordings. I have checked the weight by allowing the needle point to rest on my finger. No blood, so that will do! It's not a Goldring G800 and never will be.
The picture shows the BTH pick up with the cover removed. The top damping can just about be seen. No problem here with low output heads as this one appears to deliver around a volt!
A signature in pencil can just about be seen on the magnet clamp. Probably the guy or young lady that signed it off all those years ago.
OK so it does not play 45's or LP's but it's a whole bucket of fun! Thanks for your encouraging comments. Regards, John.

[Alex728]

Originally Posted by Heatercathodeshort

Stop it Alex. I'm very old and a rave would probably kill me.. Cheers, John.

they had a party at the local housing co-op last weekend and there were folk well into their 60s and 70s turning up (and also listening to swing, jazz etc)

though I can see why in the days of shellac records, valve amps etc it would have been more common for large installations to put the grams in an equipment room and bring the music to the people via high voltage balanced speaker lines. A while back I was sent the link to a 2kW Philips valve amp that used EL84s only as driver stages , can't remember what the end stage valves were but it had 6500V on the anodes and the service manual started off with a warning about this and "DUS WEES VORSICHTIG!" (so be careful!). As well as 100V circuits it could drive 220V speaker lines...

[Anthony Thomas]

Originally Posted by FERNSEH

The 3-3 uses the EF86 which is getting expensive. There's loads of metal 6J7 valves available and I'm sure that valve would work OK as a substitute

Instead of the EF86 how about using an EF37A or are they also becoming difficult and expensive to obtain?

Tony

[FERNSEH]

There's still plenty EF37As about I'm sure. Also consider the Brimer 6BR7 and the version with the top cap grid connection,the 6BS7. This valve could be useful for certain applications where hum pick up is a problem.
Don't forget the good old 6J7, characteristics are similar to the EF37A.
From the Radiomuseum: http://www.radiomuseum.org/tubes/tube_6bs7.html

DFWB.

[Heatercathodeshort]

The pentode first stage is in no way critical and thinking about it, neither is the output stage. Almost any straight i.e. non vari u valve can be used in this particular position in this amplifier. It does not need to be an expensive low noise valve due to the fact it is not being employed as a high gain pre amplifier such as would be required with a microphone or low level cartridge such as the Shure or Goldring.
EF91 EF80 EF184 and many more on the B9A base, EF37 EF37A 6J7[G] and again many more on the octal base. Yet again many straight pentodes are available on the B7 base if you want to go down the 4v pre war range. There is no magic brew here and the results will be very much the same regardless of the valve types used. Note, the end result should sound surprisingly good. No noticeable distortion with more than enough volume for the largest of rooms. Use the best output transformer you can obtain but by all means use what ever you have available, even pushing old television frame output transformers into service. They will not be perfect but will give good results and a valuable insight into amplifier design. Remember the project was to obtain good results from cheap valves and transformers removed from old radio and television receivers, basically just junk only one step from the tip..
There is nothing like hearing a decent sound from something you have constructed yourself no matter how crude.
The circuit is quite straightforward and conventional and requires very few component value changes to accomodate a large range of valves. If you can supply heater current for your available valves, they will probably work! Regards, John.