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Hiya folks!
Been a while since I last posted regarding my 10B restoration. It's almost done. I still need to troubleshoot an issue in the scope circuit but cosmetically the unit is looking pretty good.Lots of elbow grease. Replaced front panel with an original in great shape. Repainted transformer and tube shields.
I am posting before and after pics
Edits: 08/11/11 08/11/11 08/11/11Follow Ups:
So far the unit has good RF performance. It picks up adjacent stations from nearby Los Angeles and even Santa Barbara with no problems. The stereo decoder seems to be working also. It has all original 6JK6 tubes. So I think I will leave it as is.
Edits: 08/13/11
I'd tend to agree regarding alignment of a 10B: Truly a case of "If it ain't broke, don't fix it". That said, I'd still like to find something objective regarding 10B IF and MPX decoder alignment. All I ever see is urban myth type stuff that alignemnt required very special jigs and what-not.
The IF section seems to be nothing more than a high order butterworth bandpass filter (as opposed to the traditional resonant filter) so I wouldn't think an alignment procedure would be all that difficult to reverse engineer, esp with today's cheap computer simulation power. But no one to my knowlege has done this and published it.
The special test fixture was done, as I recall, to get the chassis up to, and held at, operating temperature. All alignments need to be done at normal "closed box" operating temperature, with all shields in place, hard to do sometimes on an open box. And the 10B area where the filter components are is below deck, closed, right?
BTW, this hold for, and includes, modern SS tuners as well. I usually warm it up, do the alignment, close box, wait a few hours, and check for changes with the box closed and warm. Then open quickly, adjust, close, and check again.
The IF alignment techniques are usually one of 3, or a combination of all 3. First, visual sweep - old way was scope and sweep generator, modern way is network analyzer of Spectrum analyzer with tracking generator. Another popular way was recently discussed at Yahoo FMTuners - the Dishall Method. See thread starting at message 68366 if you are a member there. Last, fine tuning to minimize distortion is a method usually used as the last step to fine tune once the major adjustments are made.
The method used for the 10B could have used all 3, which would require both knowledge of the normal target response (i.e. am I there?) and good test gear to do.
Bob
Interesting. Curious that the "fixture" is to maintain the chassis at operating temp. My 10B provides access to the IF filter adjustments from outside the chassis with bottom cover on but with the decorative cabinet removed.
Any comments regarding my speculation as to the nature of the 10B's IF section.
"The IF section seems to be nothing more than a high order butterworth bandpass filter (as opposed to the traditional resonant filter) so I wouldn't think an alignment procedure would be all that difficult to reverse engineer, esp with today's cheap computer simulation power. But no one to my knowlege has done this and published it...
Any comments regarding my speculation as to the nature of the 10B's IF section."
Not sure what your expectation is here. You can use modern computer programs to plot the response of an analog circuit obtained from a schematic. This is a given, and so could be done for the 10B. Is that what you are looking for?
Here's the real life problem - you can't buy components with 0.1% tolerance to build the filter. So you have to adjust it to allow for the real life components tolerance. This includes cap, resistors, inductors, and also likely tube C, L and R, which are all likely to be temperature dependent, especially using original components.
So yes, you can possibly get a target response from computer simulation, but, how does this translate to an alignment procedure? Do you own a network analyzer?
Bob
Thanks for sticking with me on this. My filter theory is very rusty.
I have two basic "questions"
1. Has it been established that the 10B IF section is indeed a series of cascaded, "non-resonant" bandpass filters providing an overall Butterworth response as the 10B promotional lit seems to imply? The schematic is drawn such that it looks like a series of buffered passive filters. Or is it just a fancy conventional resonant topology? Something else?
2. If this is indeed a series of cascaded bandpass filters, to achieve max flatness within the passband (as advertised) won't the individual filter pole frequencies and Qs be staggered in some manner to achieve the desired overall response characteristic. If this is the case, it's the frequency staggering of each section that I'd be trying to reverse engineer knowing that the overall filter characteristic was Butterworth of X order with a center frequency of 10.7 MHz and a bandwidth of say 200KHz. By knowing the frequencies for each section, one could then align each section individually to produce the desired overall response characteristic.
I don't own a network analyzer and if I did I wouldn't know how to use it in an FM IF alignment procedure. Is there info on this process? I'm not planning on getting an analyzer but I'm curious about the principles behind it.
The 10B has 6 modules labeled TF2B, but no component values. So there's no way to simulate it, without measuring the individual components to get their values. This usually involves dis-assembly unless all components are marked clearly with values.
Yes, it's what I would call a buffered passive capacitive coupled filter design. All filters are resonant, so not sure where the "non-resonant" came from, perhaps marketing people made that one up. I think you/they are thinking of comparing the 10B capacitive coupled IF filters to common inductive (transformer) coupled IF filters, as seen in almost all tube tuners.
You design the filter modules with a known input and output impedance, and make sure it sees that impedance when installed in the circuit. This sort of capacitive coupled filter is seen frequently in other solid state tuners that came later, i.e. those that used LC IF filters.
If you want to read more on this, I would suggest RF Circuit Design, by Chris Bowick. A google search shows older versions of this book may be available for download as a pdf - you want to breeze through chapter 3, Resonant Circuits.
As for alignment, I already spoke to this in the above post - Dishall method, or visual sweep with an analyzer, or both. Sure, the filter has multiple poles and zeros at different frequencies, but you can only look at the whole section by non-intrusive probing of the input and output of the entire filter section (i.e. the block of components between the two active devices, tubes in the case of the 10B). Read up on the Dishall method, I think this is what you are looking for.
Bob
The IF's are permanently aligned and shouldn't be adjusted even when changing a tube. They do state the last IF coil could be touched up if needed.The discriminator can definitely be realigned, as well as the MPX section. However, very little, if any, information is available on how to do this.
The IF filters could be recreated by modern computer software, no doubt about that. It was expensive back then due to the primitive computers used.
I have just purchased an original Model 10 (predecessor to the 10B) with the toroid IF filters on cans above the chassis. A beauty to behold. It seems to perform identically to the best 10B I had. Superb sensitivity and selectivity all around.
Picture is of the actual unit that I have. It is actually prettier than the 10B with the plated chassis.
Edits: 08/14/11 08/14/11 08/14/11
Dick Sequerra mentioned that they moved the IF coils underneath the chassis because they were getting magnetized (hence detuned) by tools used in later assembly steps.
After I purchased my Model 10. I had a few questions for him.My understanding is that, indeed, the magnetization problem occurred during assembly only. Once the unit was finally aligned, it remained this way, just like the 10B.
My Model 10 after nearly 50 years performs as good, if not better, than the best 10B I've had!
Edits: 08/24/11
Nice job on the restoration. I found soaking rusted metal in vinegar overnight helps get the scaling off, but the pitting is still there.
BTW, here's a nice link for more info on the 10B, I just posted this on FMTuners as well. Giacoma spent a lot of time putting this together.
Hi!
Excellent suggestion on the vinegar. I used Naval Jelly on the RF deck and the front hood with some success.Some good informative reading from Mr. Giacomo Puzzo. I actually got in touch with him regarding an issue I am having with the -270V line. He explains how to replace many parts on the 10B but actually never attempted to re stuff the filter cans. I may be the only one that has ever done it.
I should publish a guide on how to do it ;-)
By the way, the FM tuner info site and forum is frequented by a lot of 10B bashers including John Byrns. I do not agree with his opinion of the 10B at all.
Edits: 08/13/11 08/13/11
I don't know if you remember, but I live in your area, and also own a 10b, unrestored. (Am I glad mine didn't look like that.)
Just a minor note, the RF deck is not "chrome", but anodized aluminum, the lettering, etc, is silkscreened.
Congrats, what a magnificent job, and your not finished yet.
Gene
Sure I'm different, I use tubes!
or at least that's what Dick Sequerra has said in past interviews. Can't be aluminum since it does not rust. And this one rusts like crazy!
Very nice job!
Took a little bit of ingenuity to find suitable caps that would fit...
Nice display of good old fashion craftsmanship. Congratulations !
Just drive the thing hard, etc, etc!
Warmest
Timothy Bailey
The Skyptical Mensurer and Audio Scrounger
And gladly would he learn and gladly teach - Chaucer. ;-)!
'Still not saluting.'
http://www.theanalogdept.com/tim_bailey.htm
This was a unit so rusty that most folks would have run the other direction at the thought of restoring it!
original auction picture.
Edits: 08/11/11
*
she cleaned up very nicely. Please let us know how she sounds when you're finished with the restoration.
I'm glad its looking pretty decent. The front hood can be re-chromed at some point, although I will probably leave it as is. The RF chrome deck has a lot of corrosion and I have several ideas on how to improve the appearance. One of them is to custom cut a piece of brushed metal to cover the pitted areas and perhaps recreate the original lettering on it.So, in 8 months I have:
- cleaned the unit
- Painted tube shields and transformer
- replaced optocouplers- Replaced critical signal caps with original Siemens replacements and Vitamin Q oil caps.
- Replaced all four front wafer switches
- Replaced front panel and knobs
- Rebuilt power supply with miniaturized modern caps concealed inside the old cans. New SF4007 high speed Fairchild diodes. New Old Stock bleeder resistors. German F/T electrolytics in the negative supply.
I still need to replace most potentiometers in the scope circuit.
In all, a lot of work, but the results have made it quite rewarding in the end!
Edits: 08/12/11
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