The HH Scott 350 A MultiplexCircuitry

I've been listening some to my 350 Scott but only in mono. However my belief is that it's all stock so I'm hoping that replacing the tubes in the multiplex will clear up the noise and microphonic echo from the 6BL8. Yes, I'm getting loads of grumble and interference from the stereo selection.
An additional multiplex concern however is that the multiplex circuitry in the 350 was a compromise to the refined circuitry of the 310 E. I have procured (thanks to good Audiogon friends) the repair manuals of both the 310 E and the 350 as well as both schematics and I'm hoping/wondering if my local technician will be able to improve upon the 350 multiplex circuitry by comparing it with that of the 310 E? I was told by a friend that this is possible if I were to provide the technician with the repair manuals and schematics for both tuners but I'm still somewhat doubtful.
If anyone ( Al ? ) would shed some light on this and lend a suggestion/s for me to pass along to the technician, then I'd be very grateful. By the way, I have a Telefunken E80CF (6BL8) , A balanced pair of Telefunken 12AU7's and a Telefunken 12AT7, all Amplitrex tested on hold for payment. These I'll take with the tuner and hope that he orders the best capacitors. I want to go full force with this project to the best of my abilities.
Thanks To All!
There is a Fisher forum on Audiokarma where all of the techs hang out. The question could be easily answered there.
Goofyfoot, after taking a look at the schematics I have no suggestions to offer with respect to modifying the design of the MPX circuit to be more like that of the 310E. They are simply different animals, to a considerable extent.

And my guess is that once tube, capacitor, and perhaps alignment issues are addressed you'll be quite happy with the stock design of the 350A. Keep in mind, though, that when signal strength is weak or marginal FM is inherently more susceptible to background hiss in stereo mode than in mono mode.

-- Al
Ok, thanks Al! Yes, the band width is wider in stereo mode thus creating more difficulty in receiving the transmission. Currently I use an all-right passive FM antenna and I've found a place where a couple of channels have consistent reception quality.
I'd like to eventually purchase an outdoor antenna that I can place on the window sill of my building but it isn't anything that I need to rush into.
Also thanks Viridian, I may take a look at that other site.
Goofy foot, with my 350's I use simple rabbit ears(!) and they perform well. Just thought I'd pass that on.


Thanks Dave. Currently I've been using a Terk Edge without the amplification. I can receive the stations that are close by but have trouble with a couple of stations that are outside of the city proper. These outer stations were difficult to pull in when I had my MD 90 with the ST 2 antenna so I am looking for an outdoor antenna that's apartment friendly. I may check with a HAM/shortwave shop that's relatively close by to see what they've got on offer. Can you even believe that there's still a HAM/shortwave radio store selling icom, etc..?
The big deal here is to make sure that the unit is properly aligned- for that you need an FM stereo generator- or your tech does.

If I recall right, that unit can beat if its out of alignment- that 'grumble' you mentioned.

If its not been done in a while, an alignment of the entire unit would not be a bad idea!
I concur Atmasphere, I'm just waiting to have the tubes before I take it to the technician. I'm replacing the multiplex tubes including the audio output with Telefunken's, so I need to be with the tuner before I pay out the bench fee.
Any idea's about the capacitors, what type I'll need and where to find them?
I would try with Antique Radio Supply in Arizona- they have a pretty wide range of can-style multi-section filter caps.

I assume you are talking about rebuilding the power supply.

Otherwise replacement of other caps is not going to win you much unless they have drifted in value or have some obvious defect.
Well a bit frustrating so far. I replaced all four multiplex tubes with Telefunken's, Amplitrex tested. The 6BL8 and the 12AT7 are military grade. The balanced pair of 12AU7's tested high. I did notice an improvement and everything sounded fine as the radio announcer spoke but once a cello came in, the music sounded 'garbled' or 'aggregate like' once again.
I'm at the point where I now plan to take the tuner into the shop tomorrow afternoon and will pay the bench fee to have it fixed.
Yes- it needs the multiplex section to be aligned. The shop will need a stereo multiplex generator to do the service.
Thanks Atmasphere,
Yes, I think it will work out. I dropped of the unit today and the technician said that they'll call me after they look at it. There's about a two week turnaround but that seems reasonable. Once I get word I'll post it here.
OK, so here is the scoop straight from the technician concerning the 350 A; 'we can't find anything wrong with it so we want to give you back your bench fee and you can pick up your tuner also.'
The tech tested the tubes and caps and said they were fine but mentioned that there was significant corrosion in the outputs. He mentioned that 1 capacitor tested low by 10% but that he didn't want to replace it. I asked if he would clean off the corrosion and then have it ready for me today so I'm planning to retrieve my tuner this afternoon. The technician did agree however to come by and listen to the tuner in my home if I were to continue experiencing the issue with the multiplex stereo option.
Did they perform a stereo multiplex alignment?
No Atmasphere they did not do a stereo multiplex alignment and I told them that this was what needed to be done as well as them cleaning the oxidation in the outputs.
The technicians said they had never heard of a multiplex charger but that was after they had the tuner. I gave them a copy of the service manual and it listed what to do with the multiplex without the proper equipment but they balked. In a way I'm glad they didn't touch it, they seem clueless.
So prior to driving over to the technician to get my bench fee, I called Ryan at Audio Classics and said I'd ship him the tuner within about a month from now. Ryan said that even though it's not a tuner they typically work on, that they could do the work. And yes it will cost more but they repair the Marantz 10 B and all of the MacIntosh tuners, so I have confidence in their skill level. Also, I've been a prior customer at Audio Classics so I feel comfortable with their business practices. But what a bunch of kooks these local technicians are.
Just FWIW, we can do a stereo alignment too. FM Stereo Multiplex generators are not as common nowadays as they used to be. So it does not surprise me that a newer shop might not have that instrument on hand.
OK, so you're located in St Paul. Had you mentioned it earlier, however I make it a practice to follow through with the first person in the chain. I'll call if I plan to send it to you due to circumstances.
We are a manufacturer, and we do a lot of work in the service arena also. As a result, I try really hard not to get in trouble with the site rules.
No problem, it's just that I hadn't any knowledge about your being capable of servicing the tuner, that's all. If there are site rules about soliciting in circumstances such as these, then it seems to be somewhat counterproductive.