Why would Philco designers put resistors in some of the bakelite blocks? Weren't they potted with tar? And isn't one of the functions of a resistor to shed heat? It seems like a bad setup.
Kestas
No, heat is not the function, heat is a by-product of a resistor.
And in some cases the heat is very small and the resistor does not need cooling, so potting is totally benign.
The resistors typically were wire-wound, I measured some (I had to gut the block and so re-using the resistor was not an option) of theme and after this many years the resistance was right where it was declared, meaning it did just fine.
No one would pot a resistor that would be intended to dissipate a significant amount of heat.
As Morzh stated I don't think that heat dissipation was a concern with any resistor potted inside a Bakelite block, they were likely used in a low current application like a grid bias resistor or a cathode bias resistor for a lower current tube like an If or an RF amplifier. As yet I haven't found one of these potted resistors, all of the Philcos I have worked on used the terminals on top of the blocks to mount resistors.
Regards
Arran
Thanks for the explanations.
I have run into them a couple times and have been able to preserve them each time. They look like a little bundle of wire coiled up and enclosed in some of that grey heavy paper they used back in the day. The ones I have seen have been right on value so no point changing them so long as you don't damage them when cleaning out the bakelite block. There must have been a reason they used them but I don't know what that reason is, does anyone know?
Gregb
I also found those and preserved them. Good high resistance wire (maybe Constantan?)
Reason? Convenience maybe. After all all those Philco parts were only manufactured for own production and there was a multitude of backelite block cap assemblies; nothing wrong with putting a resistor in really. Less soldering. Probably the same reason as with cap assemblies.
Plus I think the backelite block idea itself was: you get free soldering posts to hold wires.
I have always reinstalled the original resistor in the bakelite blocks. I don't understand why some restorers make such a big deal out of re-stuffing the blocks. It is not difficult and like Mike said they provide tie points for other components. It really was a good system.
Steve
Bakelite blocks are one of the reasons I like Philco radios. They make the chassis look less cluttered and provide all those really nice tie points, and they really are not hard to deal with. The other thing I like about them is most of the local collectors avoid Philco radios because of the blocks and the cans potted full of caps. Easy pickens for me.
Gregb
I thought people didn't like Philcos because of all the open coils that are found on them.
I personally like the bakelite blocks and I like dealing with them.
Open coils? Plenty of AA5 from other companies have them. I do not mind them at all.
In fact the single thing I detest about some Philcos (and I have some of the worst to deal with RF-chassis-wise now, 37-116 and 38-690) is the RF chassis. That's a bear to deal with.
(04-26-2016, 03:59 PM)morzh Wrote: [ -> ]Open coils? Plenty of AA5 from other companies have them. I do not mind them at all.
In fact the single thing I detest about some Philcos (and I have some of the worst to deal with RF-chassis-wise now, 37-116 and 38-690) is the RF chassis. That's a bear to deal with.
What Mike said!
Gregb
We can thank (yeah, right) David Grimes for the RF units. Grimes joined Philco in 1934 and was immediately put in charge of home radio engineering and research.
I've often said...and wrote...that a fitting punishment for David Grimes would be for him to be sentenced to repairing 1937 and 1938 Philco sets with RF units for the rest of his life.
When I was a boy in college. My first professor said to us.
There are three types of engineer. Bad, Good and Great.
You wont find a bad one he said. They are Fired early on and go doing something else.
Good Engineers he said spend most of their time resolving problems left behind by other good Engineers.
Then there are the great Engineers. They design solutions without built in problems.
I guess Mr Grimes was just another good Engineer Eh.
I feel like everyone is being a little harsh on what seems like quite a clever guy when you read about him. Tragically killed during the war too so he probably never got to repair a single one. Sure, his legacy to restorers some 80 years later is a chassis that generally requires stripping to get all the caps replaced - but I'd imagine he was under commercial and personal (proving himself in a big new company) pressures to come up with innovations (probably more for marketing than true engineering reasons) and streamline the manufacturing process. Who hasn't in the past done something that seemed like a good idea at the time, eh?
And yes, I own 3 of them... 37-61, 37-630 and a 37-640.
So many radios take 10 minutes to get going again... at least Philco thought ahead and must have realised that every now and then we'd need a bit of a challenge to keep us feeling alive
As to the original question - there was one in the 89B I did... at the time it seemed like a good idea to replace the resistor envelope with a modern equivalent... but in hindsight there was absolutely no reason to have done so - it was (as most wirewound resistors are) still bang on the money. It was a combo decoupling cap and cathode bias resistor for one of the tubes from memory... so my guess is that it was put in there for simplicity in manufacturing... one less component to hand wire in to the chassis. One wire to the cathode, bolt to the chassis for ground. Done. And the middle tags are free for something else if needed. I love bakelite blocks for all the reasons everyone else above does. Neat, tidy, nice to restuff and they make the wiring neater... sometimes.
Cheers
Steve
I think great engineers simply move to architect / inventor activities and let good engineers to perfect and commercialise their results.
Because even the greatest of the design engineers will make...not necessarily mistakes, but decisions that in the long term will look like mistakes. I would not blame a guy who designed something 80 years ago. The radios simply are not required to last more than 20 years, even then they were not, and today a 5 year life span for most electronic is good enough. The only type of product I could think of that today would be required to last lobger is large appliances like washers, fridges, ranges. And they often do. One could still find 50-s fridges that possibly once were recharged in operation, and the single reason they were tossed was their style went out of fashion. I bought my apartment in 98, and it had all original equipment from 75 by White-Westinghouse, the wall air conditioners, the fridge, the double oven range, the dishwasher, the trash compactor. And it all worked.
These engineers didnot design for antique collectors. They design for general public, and their first and foremost goal was, is and will ever be (I'm one of them so I should know) to make comnercially successful product, which involves the compromise between usefulness, appeal, reliability and cost.
As an engineer I still design in electrolytic caps. I know full well they are officially a limited life span item. Best of them are rated 5000 hrs of operation at full specified current/temperatures.
Yes I choose good ones and try to design so they would last but I am constrained: say a power supply I designed for a telecom company to be deployed in India put ridiculously high requirements next to impossible to meet cost. I had to get really crafty, and this considering buying parts in hundfed of thousands at a time (total qty 2 mlns) directly from China. I am still not sure we were profitable but we met the $12 per board limit. I cannot design it to last forever at this cost.
An engineer is more than just a guy who know, say, electronics. He is a vuy who knows how to make a real product. Otherwise he still can be great at teaching or inventing, but this is not really engineering.