The Fine Things are Always Hand Made
My cousin from Arizona arrived yesterday at my place in Columbia, MO with a Scott Allwave 15 for me to restore. Doing some preliminary reading, I see in the alignment instructions that there is a special IF can cover that must be installed do do alignment. I don't have this, but I suspect I could fabricate something if I knew what it looks like. Does anyone have one they could maybe provide me a photo and some measurements?
I have also read several posts here regarding the rotary band select mechanism, and some fairly hairy horror stories. I would appreciate any advice anyone can give to keep me from falling into this pit.
Lastly, I have to replace some veneer on the front. To my eye, it looks to be walnut. Can anyone verify that?
I have already been warned that this will be a very challenging restoration, with a lot of hard lessons to be learned. I'm hoping you guys can ease the pain a little. This belongs to a very dear cousin, and I want to send him back a nice, properly performing radio.
Any help greatly appreciated
Michael - As for audio quality. My take follows.
Circa 1930, the effort seems to be chasing quality as folks were figuring out the technology. But approaching mid 1930's there were two trends: 1) pursuit of performance and 2) how to control costs (doing on the cheap). Scotts and other manufacturers produced performance with higher tube count radios. But The 4, 5 and even 6 tube radios were designed for low cost rather than performance. After all, there was the Great Depression. I am talking about superheterodyne radios.
Small tube count radios usually had no frequency preselector (no 3rd gang on the tuning capacitor), no radio frequency amplifier stage, only one stage of IF amplification, usually one audio amp tube driving a solitary output tube with a minimal sized output transformer, a small speaker and small cabinet. Putting a cheap radio in a floor model cabinet with a lager cheap speaker only helps lower frequency tone somewhat but does not solve distortion problems or design short falls. Adequate for local stations for news and radio shows like Amos & Andy or Jack Benny. Maybe a 2 or 3 watt amplifier.
Scott and other manufacturers engineered more performance with higher tube count radios. A more performance oriented radio will have a number of additional features. One radio frequency stage consisting of an amp tube together with 3rd section on the tuning capacitor to tune and reinforce the desired station and reduce interference from other adjacent stations. Two or more IF amp stages to further amplify the station signal. One or two stages of audio amplification driving a pair of output tubes wired in push-pull, a better output transformer (more iron) and a larger, better quality speaker. Usually some kind of tone control, to reduce higher frequency audio to make the audio seem richer. So these features will require an 8 to 10 tube radio, and better floor model cabinet to further reinforce lower frequency tones. Such a radio may have a 4 to 8 watt output amp in the 1930's. High fidelity in 1934 suggests audio frequency response of, say, 100 to maybe 5000 cycles.
Your Scott AW-15 has all these design features plus 3 stages of IF amplification for even fainter stations, push pull 56 triode audio stage to drive higher power 2A3 triode output tubes operating in push-pull and a theater quality 12 inch speaker designed with a ribbed surround to allow more cone freedom to handle the sound spectrum. And tuning aids like sensitivity control, tuning indicator and a beat frequency oscillator to help tuning stations. Plus, the radio was carefully designed and engineered for low circuit noise, robust construction, low audio distortion, and well over 10 watts output. The Scott AW-15 amp handles way more volume than needed for ordinary room listening, but has the power reserve to handle a loud signal (bass drum, low organ note, loud chorus ...) with minimal distortion.
The AW-23 of 1935, sported a 40 watt amp and even more features and can reproduce music louder than you can stand and sound good. With the optional tweeters and frequency response from 30 to 16,000 cycles, my AW-23 could really blast my CD of Big Bad Voodoo Daddy.
At the time it was said, if you wanted the finest radio, buy a Scott. A McMurdo Silver Masterpiece 2 or 3 would be the equal in many ways.
In 1930 with very few exceptions radio manufacturers were focused on selectivity and sensitivity, not the range of audio frequencies produced (audio range, not fidelity which refers to the accuracy of the reproduced signal or lack of distortion). There is a conflict between selectivity and audio range. Highly selective receivers have narrow bandpass characteristics that are unable to pass a wide range of audio frequencies. By the mid-1930s manufacturers were responding to demand for receivers capable of reproducing a greater range of audio frequencies and incorrectly calling them high fidelity receivers. While most receivers continued to employ high gain, narrow bandwidth IF amplifiers, some companies started employing lower gain, wider bandwidth IF amplifiers for wider audio range with some including variable or selectable bandwidth for both high selectivity and greater audio bandwidth at the users discretion. EH Scott Radio Laboratories was somewhat unique in using IF amplifier transformers for selectivity only (no gain) and tubes only for amplification, hence four stages of IF amplification in Scott receivers.
Thanks for all that. I'm aware of, and agree with all you said there. I have a 70 foot long wire that I use, and I have a rough inventory of short wave stations I can usually get. I was hoping to avoid doing a full alignment, but I think I will undertake that next. I'll let you know what I find out.
I guess that explains why some of my sets do better than others. There is probably some way to tell which radios are equipped with which type of IFs. That said, If the Scott has narrowband IFs, as you say here, they are finding some other way to deal with it, because the audio from this set is outstanding.
I think I've done about 250 radios so far, but one thing I like about this retirement hobby is there is always more to learn, and I'm learning quite a bit from this Allwave 15.
The IF transformers in Scott Allwave sets are not narrowband. They are no gain and four are used to obtain steep skirts at a moderate bandpass.
Sorry. I misread your previous post. I misinterpreted the word "selectivity" to mean narrow band. Got it now.
Norman - thanks for the nuance explanation on the IF amplifier design on the Scott.
Michael - The AW-23 of 1935-7 further developed the IF amp for variable selectivity with a shaft of small air caps below each IF transformer, to detune (broaden) each IF transformer for wide band audio reception. Worked in conjunction with treble control. The 30 tube Philharmonic of 1937-41 had a similar set up for variable selectivity.
- there are Scott News issues featuring audio quality and Scott's efforts to pioneer high fidelity reproduction. Go to the Scott Info Archive, Scott News, and, for example, August 1935. SN-8-35
I guess I didn't know Scott had made a 30 tube radio. Wow. You could probably turn down your furnace in winter if you had one of those.
Currently in learning mode. SW still dismal. BFO doesn't seem to work. Tuning acts a little funky on SW. No response necessary. I'll keep at it.
I'm stripping the cabinet right now and noticed something. There are no screw holes in the cabinet where the receiver and power chassis sit. On the cabinet framework where the receiver sits there are 5 smallish dimples, maybe 1/4" dia and 1/8" deep. I've gathered from the instructions that Scott shipped the radio in pieces and it had to be assembled when received. Were there some sort of rubber feet that screwed to the bottom of the 2 chassis' and they just sat in the cabinet? There aren't even dimples where the power chassis sits.
On another subject, my bandswitch knob was toast. These appear to be pretty much unobtainium. I have heard numbers like $300, for gosh sake. I got my friend John Gollar to send me the knob from his set. (Bless his heart, this was very kind of him.) Yesterday afternoon I took it over to a neighbor kid, who dabbles in the blacksmithing hobby. I made a dummy shaft with the correct flat on it. We sand casted 3 copies using an alloy of copper and aluminum, one of which is useless as I failed to get the dummy shaft correctly oriented. On the next 2, I got it fairly close, probably will still be off a little. After I finish stripping the cabinet, I'm going to machine off the casting lines on one of them, Then I'll install it and twist it through the ranges and make sure it is strong enough. If it passes that test, I'll drill it, sandblast it with sand then walnut shell and see what it looks like. Next I will need to see if I can antique the brass to look original. Otherwise, might have to resort to paint. While I have John's knob, we could make more of them. If any of you know of someone who needs one, we can dicker on a price depending how good the results are.
No rubber feet. It was up to the customer to bolt the chassis to the cabinet or to have the authorized Scott representative bolt the chassis to the cabinet. Most did not. Some did.
Well, I'll be darned. Never would have thought that. Thanks! I'll ask my cousin if he wants it screwed down. It has occurred to me that it was a bit of a dumb question, as there is absolutely no room for anything under the chassis around the holes for the bandswitch and beat oscillator controls.
Thanks for the info!
Michael - For the AW-12, AW-15 and AW-23. the receiver control shafts have threaded bushings long enough to extend through the 3/8 " inch front wood panel and the brass control escutcheon. Hex nuts to fit the bushing are tightened to secure the receiver and hold the brass escutcheons, sufficient to keep the heavy receiver from sliding as long as the cabinet is not tipped far.
The AW-15 amp has no flange for securing it to the floor of the cabinet. It just sits near the speaker, as per the illustration in the owners manual.
Later models had large threaded holes that would accept chassis mounting bolts, but not the AW-15.
The dimples you noted on the receiver shelf are from the round head screws that attach the bottom plate to the receiver. These screw heads digging into the wood also help the receiver stay put.