Seeburg Amp MRA5-L6 in a V200

[jeffinmn]

Just in case someone looks at this post in the future, I erred by stating I need a 7 pin plug. I need a 9 pin plug even though only 7 pins are used. It's the same base as a 12AX7 tube.  Leeds is checking to see what he has available. He lists 9 pin plugs as well but he hasn't updated his website since 2013.

[jeffinmn]

I added an RCA jack to the receiver (see Picture). It's connected to pin 7 of J1 so the volume control affects the output level. The jack is connected to the amp chassis so I did not connect a ground wire to pin 9. I used a single solid wire to make the connection (not shielded). When I connect an RCA plug to the RCA jack there is a pop or click when the mechanism changes direction and when the mech stop moving when the system as at rest. If I unplug the RCA plug from the RCA jack there is no click or pop. There is silence as there was before I made any changes. The RCA jack is near the bottom of the amp next to the 3 can capacitors in a hole that was covered by a knock out piece of metal. The auxiliary amp gets a clean signal and sounds fine as does the sound from the jukebox.

Any idea why I get a clicks when the RCA plug is in use but no click when not in use? Suggestions for a fix?

[jeffinmn]

I figured out the solution to the click problem. The pair of wires going to the auxiliary amp is shielded. The click noise stopped happening after I connected the shield ground to the RCA cable's ground. I don't know why this is necessary as I didn't use the shield ground when the MRA5-L6 amp was in use.

[jeffinmn]

I've been running the HFMA1-L6 in my V200 for the last couple of months and like the sound better than when I had the MRA5-L6 in it. One thing I'm curious about is that when the MRA5-L6 was in the V200, when the record would start playing it would take a few seconds for the volume to reach its normal level. I know this is how it is supposed to be. However, on the HFMA1-L6 the volume is at the normal level as soon as the record starts playing. I have two of the HFMA1-L6 amps and they both perform the same way. Sound is muted when the record rejects and the mech is moving but as soon as the mech releases the arm to play the record sound is full normal volume level.

Is that how these amps are supposed to work? If not, what should I check to see why this is this way?

[robnyc]

Jeff, AGC works by attenuating excess gain in the early amplification stages. If the tubes or other values in one amp are weaker thus making the early voltage stages amplify less, the AGC will take longer to reach normal average level.

In reality, the MRA amp may have somewhat weaker gain as compared to the HFMA

Some things to try:

-Exchange all tubes between the two amps except the 12AX7 and 6l6's -they don't matter to the AGC. Is the AGC action still the same-?

-The AGC time constant is C26 on the HFMA-1 (V-VL). While the mech is scanning, take quick measurements of the squelch voltage of each amp. You must take quick checks as the meter will load the circuit and bring down the reading. Then also do readings with the same record playing through each amp. If the V-amp AGC voltage readings are a lot lower it could indicate weaker squelch generation via the voltage dividers of R49 & R50 (v amp).

On tube Seeburg amps the squelch voltage will usually equal the highest playing AGC voltage of the loudest record. For SK7 circuits that will be 40-45 volts. For BJ6 it will be 25 volts. It is important that the loudest record never exceed these levels or the circuit will lose control and heavy distortion occur.

Finally, while you have each amp in place, select a slot with no record and remove the RCA pickup plug. Once the machine sets down and enters play mode, meter the same AGC time constant capacitor to make sure the AGC voltage declines to no more than a volt or two -ideally only millivolts. This area is extremely high impedance and there are several capacitors that can leak and hinder proper AGC action.

RobNYC

[Ron Rich]

On the other hand--you could support the jukebox parts suppliers listed in our FAQ's section-- I know several of them stock that plug--and maybe a correct pot ?? Ron Rich

[jeffinmn]

Ron, I bought the plug, pot and case for my remote from Durfee at needles for jukeboxes. He was very nice and found the remote case and 9 pin plug for me. I bought the 2 pin plug for the reject button on Ebay as he didn't have one. Thanks to Durfee's help and the service manual which shows how it all goes together I was able to put together a MRVC-2. I had the exact knob for the volume control on an old Eico tube tester I haven't used in years. 

I looked in the FAQ section and didn't see an area for suppliers, who I would be happy to support. I did see a market place of items for sale though. I've also purchased parts from MFFE, who is also very helpful.

[Ron Rich]

Jeff,
It's the 4th subject down ?? (PhonoLand Archive)-"Books" Parts-------
Wanna borrow a pair of glasses ?    Ron  Rich

[jeffinmn]

Thanks for the direction Ron, I found it. I'm glad to see I'v been purchasing from many of the people listed for many years.