09-11-2012, 02:12 PM
(This post was last modified: 09-11-2012, 02:19 PM by Radio Fixer.)
I like the Minerva. To me it looks like touch up rather than refinishing, or only partial refinishing (maybe sides, top?). Glad you are going to leep it light and as is.
The Tell is the earlier set and more my era. The total screening is not inusual for a TRF with two or more RF stages.
Below is an extract from a BVWS article I wrote on restoring a Philips Super Indictance set. It hopefully will explain things...
" A reasonable band pass characteristic would be roughly rectanglular in shape of between 6 to 9kHz wide. TRFs sets were trying to achieve this at every tuning position across the wavebands. For the Superhets this was not the case, as all frequencies get converted to the IF and the selectivity is mainly determined at that one frequency. In the early days there was usually a little pre-filtering by either a band pass filter or a tuned RF stage. Eventually, once they were able to make IF strips at a higher frequency, with better second image rejection, these could be dispensed with for cost reduction. The Philips Super Inductance sets have excellent coils and a design that keep a reasonable band pass shape, across the bands, and the best for this, as is to be expected, are the radios that have the two extra coils in a band pass filter .
The Superhet radio chassis can have minimal expense on screening compared to a similar performance TRF one. With a TRF chassis the gain is all at one frequency and typically they tend to be unstable at the high frequency end of the MW band. This is say 1.5mHz; lower down they can be completely stable. With this 638A, for example, it will burp and burble up there, unless the screening is near perfect (more on this later). A Superhet immediately wins, as it only has a small amount of gain at the 1.5mHz before that gets converted to the lower IF. Almost all of the gain comes at this lower frequency.
In summary:
The later and more expensive Super Inductance TRF set had four coils on glass formers in big copper cans. Each section of the tuning gang needed to be screened, and a potentiometer was coupled to it to make for a reasonably constant gain across the bands. The chassis was divided into sections with switch wafers having their own compartment. There is extensive use of screened wiring.
The Superhet radio could have coils on cheap cardboard formers in small aluminium cans. Its tuning gangs could be un-screened with no coupled potentiometer as the IF strip was essentially of constant gain (but modified by AVC action of course). Compartments were dispensed with and the switch wafers used only a piece of metal between them (performance sets) or nothing at all.
Naturally Philips covered themselves and were making a Superhet, the model 588, in 1934 whilst at the same time continuing with the Super Inductance sets. But economics spelt the end of these, wonderful as they are, and by 1936 there were no new models ."
The method of dial drive was often used on US sets of that period. From memory it gives about 30:1 slo mo reduction.
Be really, really careful how you clean the dial ... if immersing in water you may end up with 'letter soup'. Try a letter, a serial no that doesnt show is the best, and go over it with a moist cotton bud as a test
Gary
The Tell is the earlier set and more my era. The total screening is not inusual for a TRF with two or more RF stages.
Below is an extract from a BVWS article I wrote on restoring a Philips Super Indictance set. It hopefully will explain things...
" A reasonable band pass characteristic would be roughly rectanglular in shape of between 6 to 9kHz wide. TRFs sets were trying to achieve this at every tuning position across the wavebands. For the Superhets this was not the case, as all frequencies get converted to the IF and the selectivity is mainly determined at that one frequency. In the early days there was usually a little pre-filtering by either a band pass filter or a tuned RF stage. Eventually, once they were able to make IF strips at a higher frequency, with better second image rejection, these could be dispensed with for cost reduction. The Philips Super Inductance sets have excellent coils and a design that keep a reasonable band pass shape, across the bands, and the best for this, as is to be expected, are the radios that have the two extra coils in a band pass filter .
The Superhet radio chassis can have minimal expense on screening compared to a similar performance TRF one. With a TRF chassis the gain is all at one frequency and typically they tend to be unstable at the high frequency end of the MW band. This is say 1.5mHz; lower down they can be completely stable. With this 638A, for example, it will burp and burble up there, unless the screening is near perfect (more on this later). A Superhet immediately wins, as it only has a small amount of gain at the 1.5mHz before that gets converted to the lower IF. Almost all of the gain comes at this lower frequency.
In summary:
The later and more expensive Super Inductance TRF set had four coils on glass formers in big copper cans. Each section of the tuning gang needed to be screened, and a potentiometer was coupled to it to make for a reasonably constant gain across the bands. The chassis was divided into sections with switch wafers having their own compartment. There is extensive use of screened wiring.
The Superhet radio could have coils on cheap cardboard formers in small aluminium cans. Its tuning gangs could be un-screened with no coupled potentiometer as the IF strip was essentially of constant gain (but modified by AVC action of course). Compartments were dispensed with and the switch wafers used only a piece of metal between them (performance sets) or nothing at all.
Naturally Philips covered themselves and were making a Superhet, the model 588, in 1934 whilst at the same time continuing with the Super Inductance sets. But economics spelt the end of these, wonderful as they are, and by 1936 there were no new models ."
The method of dial drive was often used on US sets of that period. From memory it gives about 30:1 slo mo reduction.
Be really, really careful how you clean the dial ... if immersing in water you may end up with 'letter soup'. Try a letter, a serial no that doesnt show is the best, and go over it with a moist cotton bud as a test
Gary
