Rock Ola 1494 question

Hello to all

My name is David and this is my first post here. I am working with a Rock Ola 1494.

First thank you to Stamann for parts and help.

I have all the mech cleaned and working and now am looking at the amplifier type 36196 - A

I am in the UK and I think the jukebox is a Nova import. It has the 220/240v transformer and had a Elac KST 103 cartridge which I have changed for a Pfanstiehl P-132D.

Is there any knowledge of what other modifications Nova would have made to these import jukeboxes . I have noticed some extra resistors in the write in unit. 390 Ohm on contacts on the write in and ADR relay. Also a 270 ohm from the DC+ output to ground on the rectifier in the amplifier. None of these resistors are shown on the schematic drawings for the 1494. Are these Nova modifications?

David

Hello David,
there are several modifikationen over time even made by Rock Ola that are not documented in the schematics like reisistors across contacts or coils. However, 270Ohm from DC+ to GND im the amplifier makes no sense. Please check again, maybe kOhm ?
Rgds Jürgen

Hi David,

Maybe the extra resistors were not added by NOVA, but can't say 100% for sure.
We don't have a NOVA 1494 schematic, but one which states handwritten "1494TMS" which is this model: [www.jukebox-world.de]
This schematic in general is the Rock-Ola one but with added NOVA name on it. There are no extra resistors shown like you mention.
I suggest to check carefully what they might have been added for, what kind of sense they might make. Maybe those were added later by an operator for any reason.

A NOVA modification can be resitor(s) in the tonearm when converted to ELAC KST103. The ELAC has a much higher output than the originally used Atstatic. The resistors adjusted the output for the input of the amp.
So these need to be removed when using a ceramic cartridge like the Pfanstiehl.
Other modification in general can be NOVA amps and power supplies. But you would have realized that because they look different than the Rock-Ola units.

Kind regards - Hildegard

Jurgen
Thank you for the information. I did think that there would have been small modifications through the years that are undocumented.

You are correct it is 270k. I found a circuit diagram for a 41056-A (Rock Ola 434 ) which is a similar amplifier to mine and it shows the 270k resistor in the power circuit after the rectifier. It also shows a 2k2 resistor and 0.1mfd cap before the rectifier across the secondary outputs of the 235vac taps on the transformer but these are not fitted to mine?

I am being very cautious as the jukebox has not been used for 40 years. I have not yet powered up the amplifier.
I have replaced the selenium rectifier with a bridge package and the main power electrolytic capacitors. I will replace other electrolytics and bypass caps.

I am going to power the amplifier with the valves removed. Slowly raising the power using a variac and check the HT voltages
around the circuit. I think I may need to add a resistor to reduce the voltage from the new rectifier.

Any advice would be appreciated
Regards
David

Hi Hildegard

Thank you. I have removed the resistors in the pick up arm.

The extra resistors in the write in unit do not look like they have been added. The credit, write in and all the mech is working fine so I think they are ok. I did find a video on You Tube of the same jukebox and there was a close up inside that showed the same resistors in place.

Interesting to see from your link how NOVA repackaged the mech and electrics into very different wooden cabinets. They look like HI Fi radiogram cabinets for the home.

Regards

David

Hello David,
the purpose of the RC on the secondary side of the transformer is to reduce noise coupling from mains into the amp - small improvements of the design over time. Before powering up, make sure the correct fuse is installed, clean switch contacts and tube sockets, connect speaker and volume control. You cannot measure the supply voltages without tubes because there is no anode current and therefore no voltage drops in the filter chain.
From your comments and questions, I think you have no experience with tube circuits, you may want to consider getting professional help.
Rgds Jürgen

Hi Jurgen

Yes you are correct I am not an expert but always learning.
Maybe I did not explain my method clearly. I am powering up with the valves removed with a low power input to check that the wiring is ok with no shorts to ground and checking for voltage presence at points in the circuit. I am not looking for correct v at this point. So sorry I should not have said checking HT ! Of course conditions will change with full voltage and the valves in place but I hope to eliminate wiring issues first.

I really would not want to turn on at full power input and risk the output transformers.

All fusing is correct and anything that can be cleaned is.

I have had experience building and operating low power 100-500w valve based transmitters so I am aware of the dangers of HT

Regards David