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Old 6th Aug 2003, 5:40 pm   #1
fableglade
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Default Columbia 357 Condenser Block (Jubilee 1935)

I recently started restoration of my Columbia 357 wireless set, this set was made in 1935 for the jubilee and has what I am told is referred to as the 'Jubilee chassis'. Virtually every one of the condensers in this set is in a very large pitch sealed condenser block on top of which are mounted most of the resistors for the set, so it's housed in a pretty large assembly.

When I intially worked on the set I replaced all of the condensers that could be easily got at, checked the resistors, windings and so on and just hoped that the condenser block would possibly be ok. However when the set was powered up the signal was very weak and distorted, so I knew the condenser block had to be done.

I examined the chassis closely, the appears that the condensers were sealed in their casing with pitch together with the terminals and then the resistors were added later. I realised that if I were going to take the condenser block to pieces I would have to remove every resistor and every wire, a job that I was not overly keen on doing as this is a rather complex set and there are a LOT of resistors and leads.

I decided to leave it until the next morning and then attack the job, so I just sat in the evening and read through the service data on the BVWS CD ROM. After reading it the second time I noticed that it said the condenser leads came through the pitch and were connected to the terminals on the top of the pitch block.

I took the chassis out, removed the side panel of the chassis (4 bolts) and examined the block very closely, and I noticed that by each terminal where a condenser should be connected there was a small lead covered in sleeving which went down in to the pitch filled box.

I then decided to try disconnecting the condensers, one at a time, by snipping off the small sleeved leads, and then soldering in a modern condenser and losing this discreetly in the chassis, I did about 3 and tried the set and it was amazingly improved. I then went ahead and replaced the whole lot, there were a lot of 1uf condensers in the condenser block and even such values as 3uf and 4uf, for these I used modern day electrolitic condensers. I took one end of each condenser to the correct tag on top of the condenser block (making sure I had cut the origianl sleeved lead from the condenser block) and took the other side of the condenser either to chassis or to the correct terminal, I used the circuit diagram from the BVWS CD ROM to do this.

Once all of the condensers in the condenser block had been replaced I tried the set and it now sounds wonderful. I soak tested the set for some hours and it remained crystal clear and true.

This may not work with all condenser blocks but for this set it has worked wonderfully and the modern small condensers are descreetly hidden in the chassis and don't really show. The result is that I now have a very nice set which works superbly and I did not have to take the entire condenser block apart, so in a way it's nice to have the original condenser block intact and still in its correct place.

Others may well find this a much easier solution to what could have been a real headache. I would just say though that it would have been impossible to have done this without a circuit diagram of the layout of the condenser block together with the original values of the condensers housed in the block, so the circuit diagram is essential before starting a job like this.

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Old 13th Aug 2003, 4:05 pm   #2
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Default Re: Columbia 357 Condenser Block (Jubilee 1935)

Since posting the above a frind has contacted me to say that he has approached his Jubilee set by using this method and has had complete success, the condenser block on these sets is so involved that this does offer a much easier and perfectly acceptable way of overcoming this problem.

The same chassis layout and condenser block seems to be present in a number of HMV and Marconi sets from Circa 1935.

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Old 13th Aug 2003, 6:33 pm   #3
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Default Re: Columbia 357 Condenser Block (Jubilee 1935)

It does leave the set more original, and can be reversed, which some people view as being desireable.
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Old 15th Aug 2003, 8:00 am   #4
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Default Re: Columbia 357 Condenser Block (Jubilee 1935)

That's true.

I have to confess that the initial reason for doing this was to avoid having to pull the whole assembly apart, however the fact that the whole original assembly is now intact is certainly a bonus, and the fact that modern components are quite small they are also quite easy to loose beneath looms of wire without any major problem.

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Old 31st Aug 2003, 10:12 pm   #5
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Default Re: Columbia 357 Condenser Block (Jubilee 1935)

For anyone considering restoring one of the EMI receivers that used the "condenser block", they might be interested to know/be reminded that an article appeared in BVWS Bulletin vol 20 No 6 specifically about the blocks.

It was written by Gerry Wells (with Carl Glover) and describes the practicalities of re-building the blocks, and also theories on how they came about. It is suggested that Marconi/HMV/Columbia were concerned that their receivers were getting a poor reputation for sound quality because untrained "poke'n'hopes"; were replacing bits here and there with obvious detrimental effect to sound reproduction. The condenser blocks made it rather harder for the "helpful neighbourhood enthusiast" to interfere.

It's well worth a read.

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Old 13th Dec 2003, 11:41 am   #6
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Default Re: Columbia 357 Condenser Block (Jubilee 1935)

I was very interested to read this post as it has answered my recent query about replacing these higher value paper caps (1-3 uF) with modern electolyic types.

I have the same type of condenser block in my set (630 columbia RG). Access looks a lot easier than as you described for your set, so I will attempt to melt out the pitch and place all the caps internally, but will there be any problem with overheating?

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Old 13th Dec 2003, 2:32 pm   #7
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Default Re: Columbia 357 Condenser Block (Jubilee 1935)

I hope you get on well with it. I don't know about the overheating issue; if you intend to re-fill the block with pitch then you may have problems. The method I have described above has certainly worked well for me on two sets now, and also a friend of mine has had success using the same method, it also leave the original block intact and original.

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Old 13th Dec 2003, 11:32 pm   #8
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Default Re: Columbia 357 Condenser Block (Jubilee 1935)

Yes, I could put all of the replacements caps externally without too much visual impact, and this would indeed save alot of work, but as the leads for all the block individual condensers are internal (only the tags show) on my set, this would not isolate possible internal shorts

Regards Graham.

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Old 30th Jan 2004, 9:00 pm   #9
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Default Re: Columbia 357 Condenser Block (Jubilee 1935)

If you look closely at the condenser block you should see tiny sleeved wires coming out of the condenser block which are connected to the solder tags, if you snip them off completely the entire block is then disconnected and so remains there purely to keep the set original, it no longer has any electrical connection.

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Old 27th Feb 2004, 10:57 am   #10
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Default Re: Columbia 357 Condenser Block (Jubilee 1935)

I rebuilt the condenser block on an HMV 443, using polyester capacitors throughout. If you use electrolytics, be very wary of the polarity which is not what you would always expect. I dug out all the innards, which gave me a major supply of pitch which I have since used for restoration of many paper capacitors. I dig out the old guts, put in a modern polyester type and then seal both ends of the original tube with said pitch. I did not refill the HMV condenser block with pitch or wax to hold the components, but supported the replacement capacitors on thick wires as 'busbars'.
Nigel

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Old 27th Jul 2004, 6:29 pm   #11
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Default Re: Columbia 357 Condenser Block (Jubilee 1935)

I've also used the thick busbar type wires in some Murphy condenser blocks, it works well, Murphy blocks are usually easier as they don't have numerous resistors soldered across the top of the condensers as the EMI sets do.

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