[etech]

Hi all,

I have often wondered whether anyone has compared the performance of the code 121 chassis against the code 125 chassis of this model or even the 37-116 code 121? I know that it is commonly believed (and I agree) that Philco cut some corners on the rf deck of the code 125 chassis, since there are about a dozen compensator's left out of the code 125 chassis.

I have a code 121 chassis here and also a code 125 chassis neither of which has been restored as of yet. But, after looking at them closely, I discovered something which is very clear on the schematics but which I had failed to notice previously. That is, the codel 121 chassis all use a three gang single section tuning condenser. All of the code 125 chassis use a three gang dual section tuning condenser. I don't think I have seen this style of tuning condenser used in consumer grade radios before. I have seen them many times in communication receivers. I also noticed that the code 125 chassis use a different coil set and a differently calibrated tuning dial. It would seem that the proper 'Q' and possible dial tracking would be easier to achieve with the smaller tuning condenser used on the higher bands.

So, this latest discovery has peaked my curiosity. I wonder if there is actually a difference in performance between the two chassis? Or could it be that the Philco engineers discovered a better way to accomplish the same task? It would seem that if their primary interest was to save money, that they would not have increased costs by using a much more expensive tuning condenser in the set. Furthermore, I noticed that the number of adjustments on the broadcast band is the same in both chassis. It is only on the higher bands that the code 121 chassis have all the additional adjustments. It appears as if the additional compensators were added to try and get the radio to track properly across the band. Maybe with a dual section tuning condenser and a different coil set, the additional compensators were not needed? I don't know?

I'm just posting this for discussion if anyone cares to comment or offer an opinion.

Best regards,

Ed

[TA Forbes]

Hello, Ed: I have long believed that part of the reason the model 44 performs so well for a mere 6 tube set is the 4-gang tuning capacitor it uses. Therefore it would not suprise me to learn that what you surmise is exactly the case.

[etech]

I had a chance to looking at the model 44 schematic and yes, it is the same type of arrangement.

Just to clarify a bit, the 38-116 code 125 chassis uses the three gang, dual section per gang tuners, where there is a large section and a smaller section on each gang. Both sections are used in parallel on the 'Range 1 - Broadcast Band' and 'Range 2 - Lower Shortwave Band'.

Only the smaller section of each gang is used on the remaining three 'Ranges -Upper Shortwave Bands'. I believe that the 38-690 code 125 sets have the same arrangement.

When I get these restored, I may have to try this for myself and report back.

Ed

[Ron Ramirez]

Ed

Great topic idea!

You may (or may not) know that the 38-116 Code 121 and 38-690 Code 121 use the same RF unit as the 37-116, 37-675 and 37-690. I suspect Philco had several of these RF units left over, and used them up in early production of the 38-116 and 38-690.

In fact, it seems that I read somewhere that they did do this on purpose, to use up excess stock, but now I do not remember where I read it...if I did, that is.

Anyway, what I will call the 1937 RF unit only has, as you said, a three gang tuning condenser but has a multitude of trimmer/padder adjustments, to allow for more precise alignment on all five bands. The 1938 RF unit (Code 125) has significantly fewer trimmer adjustments. Easier to align...but may not be as precise as the 1937 RF unit.

And, yes, the 1938 RF unit does have the dual gang tuning condensers in which only the smaller sections of the gangs are used on the higher SW bands.

I no longer own any of these models, so I can't do the side-by-side analysis. So...we're relying on you, Ed.

[etech]

I no longer own any of these models, so I can't do the side-by-side analysis. So...we're relying on you, Ed.

OK Ron, will do. It may be a while though, as I have quite a few radios before these in the queue.

Ed