The Fine Things are Always Hand Made
The bass control on my MPVI is totally non-functional. I can't even get resistance readings with contact directly to the resistance elements. I can't determine if the 2 ganged controls are linear or audio taper. Does anyone know? The parts list does not say, nor does the schematic. Mark Oppat will make a new control but needs to know the taper.
Thanks in advance for any expert knowledge!
You might try a search on this site for McMurdo Silver. May be helpful.
There have been some MS threads.
I suspect (but don't know for sure) that you'd want an audio (log) taper for the bass control. A linear control is going to change very rapidly - the "useable" control range will be very limited. On the schematic for the MP VI, it is P3a/b (dual pot, as you noted). The values according to the parts list I have are a 100K and 1M ohm. So I'd see if Mark can make you a 100K/1M audio taper setup for this. The wiper connected to the LC circuit off the volume control tap is the 100K pot.
Thanks Kent. I have a control on order. I was playing with it using a 300K audio for the 1meg. Most of the bass control happened in the last 1/4 of the travel. Not sure what a 1 meg will do.
I also asked a friend (Jon) who is a very experienced high end radio restorer and has restored McMurdo Silver models, including recently an MP6, to see what he can add. Meanwhile I think Kent's suggestion is on point.
I have emailed Jon but have not received a response as yet. I also have a MP V that I purchased from him and have met him.
I've been playing/experimenting with the bass control system. The 100K control is, as Kent said, connected to the volume control. itis the typical bass compensation circuit using a tap on the volume control. The thing I don't like about it is that when the bass control in in the max position, the compensation network is tied to ground through a 5K resistor. THis cuts the treble dramatically. I suppose it makes the bass appear to be bigger but it it is not a good sound. i've fixed the compensation at a particular level by putting a resistor in series to ground. I may actually leave it this way as the bass control (with the improper control) now boosts the bass without changing the treble. I'll see what a new control brings!
Robert - interesting resolution on the bass control. Kudos, especially that you like the result.
In a related vain, E H Scott seemed to shy away from bass emphasis, as reflected in the mid 1930's Scott radios in my collection. I find I have to listen carefully for the low register sounds - they are clear and they are not at all muddy, but I wish there was a bit more bass available. With my 5 knob AW-23 of 1935 (Laureate Grande), I prefer a portable disk player with the mega bass feature into the phono input for music. My 7 knob AW-23 (Roslyn) seems a bit better in this regard. In contrast, my 14 tube Scott Masterpiece (1940/ Scott Mayfair credenza) sounds great with a normal CD player to phono input.
I received your voice message, apologies for not returning your call sooner. Dave had also contacted me mentioning your question here on the forum. I still have the customers Masterpiece VI here at the house. Let me retrieve the tuner chassis and I can submit values here on your topic, as well as pictures of the current set up.
Will be back soon,
Thank you Jon. Your pics are helpful as they confirm a couple of components that are there but don't appear on the schematic. The schematic and parts list calls the one a 1 meg pot not a 500k. But, my testing would say that aq 500K would work better.
Glad to help Rob. Good luck on your rebuild!