Deccamatic Record Player

[Ian from Bungay]

Hi,
I have aquired a Deccamatic record player with a BSR Monach Deck which works ok. The trouble is that it plays and I can hear the sound of the record at low volume, but on turning up the volume it stays at the same level. It has three valves.The 6J5 GT was loose and looked broken so I replaced it with another used one but no change.All the wires look secure. The other valves are a 6V6 GT and a 6X5 G, there is one capacitor.I would be very grateful if anyone have any suggestions. I am not an expert with these but would like to get it working properly again.
Thank You
Ian

[Chris55000]

Hi!

This would be a basic two-stage triode-beam-tetrode amplifier with single-ended output. I've not got a circuit handy but the principles are easily enough sorted!!! Proceed as follows:-

1) Trace the leads back from the speaker - these will lead to a small transformer mounted on the chassis or speaker baffle-board. this will have four or five tags on it. You'll need a good digital meter for the following tests.

a) Switch the amplifier on. Check all three valves are glowing, and watch the 6X5 for any signs of flashing or sparking inside - *switch off at once if this happens!* Look at the 6V6 - there should be nothing glowing red hot except the central heater/cathode assembly in the middle, and likewise with the 6J5 - (Note - if you've got a metal 6J5 you'll have to rely on feeling it to see if it's getting hot.)

b) Put your ear close to the speaker, you should hear a gentle low-pitch hum in it if you turn the volume to maximum.

c) If you can't hear any hum you'll need the meter for the next tests. Look at the underside of the valve holders - they have 8 pins with a central spigot hole and a keyway that a raised keyway on the middle of each valve matches up with - the two valveholder tags either side if the key are nos 1 & 8.

d) Clip the black lead of your meter to the amplifier's metalwork and count *clockwise* from the keyway of the third valve (6X5) and check the following are present:-

Pin 3 (a') 250V AC (or near to); Pin 5 (a") 250V AC (or near to); Pin 8 (k) 250 to 280 Volts DC. You should have 6.3V AC between pins 2 and 7 - (note pins 2/7 are the rectifier heater and may be connected to pin 8 rather than chassis to prevent the HT voltage being across the valve's H/K insulation)

If these are low or missing you have a faulty mains transformer or the 6X5 has failed. *Make sure the transformer is not dripping pitch or wax suggesting a HT line fault or transformer failure!*

e) If this is OK so far proceed to the 6V6 and measure the following:-

Pin 3 (a) 240-250V DC; Pin 4 (g2) 200V DC; Pin 5 (g1) Zero Volts DC (you should get a crackle or buzz in the speaker when you touch this tag); pin 6 not used; Pin 8 (k/bp) 11-13V DC.

Pin 8 is *very inportant here* as it indicates the state of the 6V6, a voltage much lower than the figure I suggest indicates the 6V6 may be faulty. If the voltage on pin 4 is low or missing the valve will be inoperative! If the voltage on Pin 3 is missing check on the tags of the small speaker transformer you located in step 1) above - two of its tags (the primary) should have the 250 V HT supply on them - a voltage on one tag only indicates a faulty LS transformer.

f) Proceed to the 6J5 and measure the following:-

Pin 3 (a) 60-120V DC, Pin 5 (g) Zero Volts DC - (you should get a much louder buzz or crackle at pin 5 0f this valve as it provides a stage of amplification); Pin 8 (k) 1.0 to 2.0V DC.

The most common fault of all in valve amplifiers is the triode-stage (in your case the 6J5) anode load resistor typically 100-330 Kilohms (coloured brown-black-yellow, red-red-yellow or orange-orange-yellow) going very high in value or open circuit! A low or zero voltage at pin 3 of the 6J5 confirms this!

2) If all the above tests suggest the amplifier may be operating, you will have to trace the connections to the cartridge-unit fitted in the back of the pickup arm - manufacturers have to use very thin leads here to prevent the arm skating across the record and damaging it, and breaks in the fine wires connecting the pickup to the amplifier are very common!

Let us know how you get on & we'll advise further!

Chris Williams

[Ian from Bungay]

Thank you for all of this information Chris , I will work through it all and get back to you.

Ian

[Ian from Bungay]

Hi Chris,

I have checked this over and there is an audible gentle low pitched hum, the valves are glowing ok although the 6J5 was loose and the metal base fractured so I have replaced it with another used one. The wires from the cartridge looked as though they had been badly soldered at the point where they connected to the wire that lead to the on/volume switch so have redone these. I still have no sound from the loudspeaker although there is sound from the needle end of the cartridge.I have rechecked all the wires and they all seem connected.

Any more ideas?

I have also ordered new stylus in case the old ones were worn out and will try these out when they arrive.

Ian