Rockola Princess 1493 Stereo Speaker Balance Problems

Hi all,

I am having some problems with my 1493 operating in stereo mode with speakers connected. The sound is loud on the left side with very little coming out the righ speaker. I have turned the balance adjuster on the amp and the sound can be controlled well for the left (good side) but has little effect for the right side. In mid position nearly all volume is on the left.

Does anyone have any advice why this is happening? Is it a valve problem? If so which one. May be a capacitor, balance control problem or just a poor contact somewhere???.

Any help will be appreciated but please note my electrical engineering knowledge is limited.

Many thanks,

ourjets

Hi, Sounds like you have a complete channel out. What you are hearing is crosstalk (bleed) from the good channel. If the amp is original, it will be due a re cap anyway, at the very least the electrolytic capacitors will need changing. You can swap the valves to see if they are at fault. The balance control is an unlikey suspect.

Hope this helps,

Nick.

Thanks Nick.

To try the valves which ones would I swap over. Presumably there will be some that are identical and can swap these.

Also which are the electrolytic capacitors. Not that familiar with this amp.

Thanks,

Neil

Hi Neil,

Make sure power is off. Swap the 2 pairs of 6793's

Make sure all valves are in correct position, properly seated and do not run the amp with missing valves.

See if the sound is restored or you have output to previously bad channel.

If capacitors are faulty then you will need a repair or some electrical experience.

Where are you located?

Hello Neil

It is also possible that the pickup is defective. The crystal cartridges from this time are very often broken, most had to be replaced already. You can easily test if your problem is on the pickup or amplifier. For this you pull the input plug from the amplifier, while playing a record. Then you take a piece of bare wire and poke it successively in each of the two holes in the socket. It should sound a loud hum. If the amplifier is working well and the balance control in the center position, the hum would be in both cases approximately the same volume. If that's the case, the amplifier is OK and the fault to search at the pickup or the pickup cable.

If at one hole appears no humming or a much weaker humming, the amplifier is to repair. You should not try to repair the amplifier yourself, if you do not have the necessary knowledge. In the amplifiers are voltages up to 400 VDC, and working on it can be very dangerous.

Best regards - charly49

Hi,

I just tried swapping over the valves as suggested. I swapped the 2 left most ones over and got an improvement on the right channel - a bit louder. Does this mean that one of the valves is faulty?

Could it be anything else too?

I am based in Doncaster England.

Many thanks.

Hi

Thanks for your reply. Excuse my ignorance but whereabouts does the pickup plug into the amp? I cannot see anything labelled that suggests this.

Many thanks,

Neil

Hello!
The best is, you follow the Cable from the Pickup to the Amplyfier than you see where is it pluget in.
mgh Willi!

Hi

does anyone know where I can get new valves (6793's) from in the UK?

Many thanks,

Neil

Hi!
Try it under this Link. You can get it also in the Shop by Stamann.
[www.jukeboxparts.co.uk]
mfg Willi!

Hi Neil, Are you certain it is the output valves?

If it were the only cause of the fault it would have reversed the problem?

If you are certain i have some reasonable used 6973 tubes.

Nick.

Hi all,

What I found is that the four tubes are all 6CZ5. Three are by GE and one is by Raytheon. This mismatch could be causing an imbalance on the stereo I guess.

What do you think?

Neil

Hi!
You can let this Tubes but you have to connect Pin 1 with Pin 8.
mfg Willi!

Sorry Jukebox Willi - I dont understand. Are you saying a mismatch in manufacturers is OK? 3 are by GE and one is by Raytheon. Are 6CZ5 tubes OK on this amp?

Thanks,

Neil

Hi!
This Tubes are ok. Its no Problem because the Tubes are from different Manufactures but you have
to control the connection between the Pin 1 and Pin 8 you must have a connection between 1 and 8
by this Tubetype. Normally by the Originaltube 6973 is the Connection 1 and 8 in the Tube inside.
mfg Willi!

Hello Neil

The 6CZ5 is very similar to the 6973, but not identical. It has slightly less power and the screen grid (g2) is only connected to pin 1. In 6973, the screen grid is connected to pins 1 and 8. If the wire on the valve socket is connected to pin 1, no change is necessary. But if the wire goes to pin 8, it must be soldered to pin 1 You can also, as said Willi, connect pins 1 and 8. This must be done at each of the four 6973 bases.

In a push - pull amplifier, the two valves (each for one channel) must have equal values as possible. The more accurate the values match, the less distortion is produced. It would be best to use matched pairs. A jukebox is not really a hifi equipment. Therefore it is sufficient if you use valves from the same producer and same-aged. In any case, you should avoid to mix old and new valves in the same power amplifier channel.

To your original problem (one channel does not work): The pickup cable has a round plug connected to the amplifier. The socket (I think labeled INPUT) has two holes, one for each channel. If the hum is very different when poking into the two holes, the amplifier is faulty. You can try to swap the valves from one channel to the other, not only the 6973 (or the 6CZ5), but also the 12AX7 and 6CY7. If the hum goes from one hole to the other thereby, probably a tube is defective. The input valve 12AU7 can not be tested in this way because it's there for both channels, one internal system for each channel.

Even if only a valve is faulty, I would recommend you to check and if necessary to repair the amplifier by a qualified technician.

Best regards - charly49