Tannoy 78 rpm record player

[Hartley118]

Originally Posted by Silicon

That mystery bulb may be a Barrettor thermistor to enable the amplifier to be used on AC/DC mains.

The barrettor will regulate the current through the 300mA heaters.

Those 13V valve heaters appear ideal for parallel operation directly from a 12V battery, but the presence of the barretter implies a series heater chain, as does the alternative mains input option. I guess that the rotary converter or similar in the separate power supply unit probably converted from 12V battery up to 230V for both heater chain and HT.

Martin

[ms660]

Originally Posted by John_BS

The L30 / H30 appear to date from 1934. Can anyone find a pin-out for the B30?

John

The data for the switch settings for the B30 is given in the Avo Valve Data Manual for valve testers (Page 83):

https://frank.pocnet.net/instruments...AVO_VDM_17.pdf

The settings are 461 237 400, from that I've deduced (rightly or wrongly) that the pin connections for the B30 valve are as follows for the B7 valve base:

Pin 1=g(1)
Pin 2=a(1)
Pin 3=k
Pin 4=h
Pin 5=h
Pin 6=a(2)
Pin 7=g(2)

Based on the Avo switch data given in this valve tester manual here (Page 2):

https://frank.pocnet.net/instruments...AVO_VDM_17.pdf

Any errors then guilty as charged.

Lawrence.

[crackle]

I love the phrase on the Cecil Marshall label "Kindly treat it as though it was your own" could be misinterpreted by any potential thief.

Mike

[barrymagrec]

Originally Posted by Hartley118

Those 13V valve heaters appear ideal for parallel operation directly from a 12V battery, but the presence of the barretter implies a series heater chain, as does the alternative mains input option. I guess that the rotary converter or similar in the separate power supply unit probably converted from 12V battery up to 230V for both heater chain and HT.

Martin

A series heater chain and the apparent lack of a mains transformer also infers a live chassis - lovely for a PA system under an awning on a wet day......

[John_BS]

Thanks to everyone for feedback, especially Lawrence for data re. B30.

I guess one reason the B30 might be very rare is hinted at by its price: 35s!

I might take along a valve tester and see if any of these valves are actually working.

The heaters most likely won't be in series as the instructions mention a pair of croc clips for the 12V battery. Ditto the "Convertor" with a 10 pin plug, and the presence of a full-wave rectifier valve in the deck, so the mystery bulb needs further investigation.



John

[John_BS]

Last week I collected the player in order to have a "proper look". I just hope those woodworm don't decide to decamp inside my shed

It's now obvious that this player has been "got-at" and modified to work from ac mains. In place of twin (12V) croc leads, there's a long captive cotton-covered light flex with bayonet light-plug attached. This connects to twin Octal rectifiers 25Z4G in place of the B7 U30.

The barrettor is an Osram 303, but as it's loose in the cap I can't screw it out.
The main HT smoothing cap is relatively modern and is not a pretty sight.

I guess we now have a live-chassis player, so The Modifier (perhaps better named The Terminator?) has thoughtfully disconnected the wire which used to bond the main valve chassis to the top deck.
I've now tested all the valves, as follows:

DH30 just OK (60%)
L30's both excellent /100%
25Z4G's fine
B30's. Well, herein lies a tale. Wired up according to the AVO data, absolutley nothing on the CT160 on all four triodes (heaters glowing nicely).
I then resorted to trying to measure electrode capacitances in order to check the pin-out. Cathode was easy (to heater c. 13pf) but everything else to cathode was very similar. Looking at the wiring under the chassis gave clues to seperate the anodes and grids (anodes all wired across in parallel betweenthe two valves, cathodes direct to ground, no resistor ).

I tentativley ran up the first valve using the new settings, and now measured some anode currents, but only c. 7mA (spec. 30), so these B30's are pretty much expired.

(For information, the correct settings are 4462317 )
Given the state of the cabinet, the amateur modifications & the lack of either the speakers or the "invertor" unit, my feeling is that this might best be scrapped for parts? or is there someone on the forum who would really fancy restoring this?

John