V200 HFMA1:Suppression of Interference by Read Out circuit??

Hi Ron,

After your help with fixing the Mech on my V200D, a few weeks ago, (MECH runs perfectly now), could I ask you another question?

Background
The V200 Tormat Selection Receiver TSR1-L6 was modified early in it's life by the Operator to a TSR3-L6 Read Out circuit (no PL2D21 Thyratron, but direct Read Out); Write in & Trip PL2D21 thyratrons, as before.
I was told by a local Service Engineer (many years ago) that All V200's were modified here in such a way (presumably by instruction of the Seeburg Importer in Rotterdam).

My HFMA1-L6 AMP runs fine (Nice Jukebox sound especially on old singles), but runs without AVC (6SK7 tube removed).
This was done by the local operator, as well, presumably because the stero needles for the Redhead (TONAR DS 88) give less output than the original Pickering Mono spikes.
(I did try a 6SK7 but I had to crank the volume pot higher, which then results in less BASS due to different (less favourable) position of the loudness) -> gone is the nice JukeBox sound.
(No worries to leave out the 6SK7 tube, since I do not need AVC anyway).
BTW The Mute switches on the MECH work allright (as well as the Ms squelch switch).

Now the question:
I always had a ticking sound out of the speakers whilst scanning (caused by the Direct Read Out, see above) and picked up by the Amplifier. (READ OUT itself working fine).
The amplifier is properly muted during scan; the interference noise (in the speakers) is picked up by the AMP (no interference noise if the 5U4 GB recifier is pulled out).
The interference is picked up AFTER the volume control, because this does not influence the ticking sound. Hence the Mute does not kill this interference either (is applied before the volume pot).

I read in Dr. Hagens book that this problem could be cured in the KD200, by putting a 10K resistor in series with the grid of the first triode after the volume control.
Can you advise whether this could work in my case (HFMA1-L6 as well)?? Any other MODS??
Could you please attach a part of the schematic, showing the proposed modification(s)?

Many thanks for the help!

Greetings from the Netherlands!

Mart

Hi Mart,
Sorry--I don't understand what modifications were done to the TSR-1 ? Did they add the choke onto the detent switch ?
As for the clicking--most of the time that can be "cured" by cleaning ALL "ground" (earth) connections in ALL plugs--Also, make sure the 5A fuse on the front of the mech is well connected, and the screws on the TMU "grounding bar", are tight--NOT "over-tight" !!.
I have never attempted to add the resistor on anything except K/L models. On these, all one needs to do is "cut the trace" ( remove the wire[s?]) going to pin 7 of the 12AX-7 tube in the circuit, just prior to the 6L6's, and add the resistor to the pin, with the trace (wire[s]), now going to the other end of the resistor ( In series).
Let me know if that helps--
Ron Rich

Hi Ron,

Thanks for the advice!

I have this V200 box already for many years and it has always been ticking via the speakers during scanning.
I can see that a modification has been done to the TSR-1L6, because one PL2D21 tube is missing (Read Out) and I could see some (not so nicely laid out) wiring mods. There is also a "new" choke under the chassis, but not on the mech (cannot see a 5 Amp fuse either there). But since the box selects well, I do not want to touch it (don't change a running system)!
I will check the earth connections, as you advised and I will try the 10 K suppressor resistor in the grid of the V6: 12AX7, as you and Harold have done in the KD200's.
However, the High Fidelity Master Amplifier (HFMA1-L6) is different compared to the KD200 (no printed circuit board). Would it therefore be possible to show (part of) the schematic of the KD200 amplifier so, I can understand how this added 10K resistor would "translate" for the HFMA-1? I enclose the diagram of the HFMA1-L6, for reference.

It's getting spring over here, so maybe it 'll take some time before I report back!

Thanks again!

Martin

Martin, you can get a schematic for the K here: http://www.verntisdale.com/Seeburgschem.htm

Other points:

Try connecting a clip lead from pin 3 on the mute socket to the chassis ground. If the the clicks go away, see if there is measurable resistance from pin 3 to ground in normal muted state with mech plugged into it.

AGC, in theory the AGC should have negligible effect if output from the cart falls below the minimum point where useable control voltage is produced by the 6SL7. With the machine in play mode and no record there should be little-no voltage on time-constant C26 (1mfd). Check also at pin 4 (grid) on 6SK7 socket. If you find more than a few volts under those conditions it is likely that there is poor grounding occurring at pin 2 of the mute plug during play thus allowing some squelch voltage to reduce gain, or there is a leaky cap associated with the SK7 grid, most likely C24 or C27.

There is another possible cause of poor bass when using the AGC; since you are using what is likely a ceramic sub for the original cart, it will be reactive working into the 100k-ohm load presented by the input. Under these conditions the low impedance further reduces what is likely poor low end response from that cart and only the massive bass boost in the first 1/3 of the volume control can (somewhat) compensate for this.

I've never seen any"DS" carts (ceramic) that were better than mediocre in these applications. The best approach is to go to a magnetic pickup as the system was designed. -If- the new European styli for the Redhead cart are as good as they claim, that would be the easiest/simplest way to much better sound and be able to use the AGC if so desired. Not cheap, but the results will definitely better than what you are using now.

Rob/NYC

Hi Rob NY,

Sorry for the late reply. I will follow up your checks.

WRT the cartridge: This is still the original Pickering HiFi Magnetic "RedHead"/

In the NL there were (and still are substitute) stereo needles by the Brand TONAR (a needle manufacturer).
The 188DS ("Diamond Stereo), is the normal stereo compatible used, they also had the usual Seeburg Mono spikes.

I have to upgrade this AMP ( I changed some capacitors) some 15 years ago (but not the Elco's ). By now they must have dried up, because the amp hums more than it did.

Time for a rebuild on a rainy day.

Cheers,

Martin