valve Radios and valves

[aks07]

Respected Rajan Sir

It is extremely good fortune to see you here. It has been a very long time since we corresponded. I just sent an email at your yahoo ID.

Hoping that interested forum members will archive Rajan Sir's advices on how to restore and maintain a valve radio with an Indian context. This type of skill set is increasingly rare specially in Indian discussions forums.

Warm regards
AKS

Uh oh you mean you won't help me in getting it restored!:sad:

Dear Captain Sir

I believe what he meant is:

1. Restoring an AC/DC on purely technical merits is not worthwhile. It is a different matter if sentimental values are attached to the radio.

2. AC/DC sets were a cost effective alternative for fully AC radios. The AC/DC sets were built to a price point and it shows.

3. They are inherently unsafe. Today I would not like to have such a contraption around house that has the potential to kill someone. Back in the days one of our acquittance was fatally electrocuted when she accidentally touched the antenna wire in the roof.

4. Converting to AC operation is very cumbersome. Essentially you are rebuilding a new radio set. This will involve changing some of the operating points which may require realignment and such. I've never even attempted such a conversion.

Today would I restore an AC/DC radio? Only if this is the last valve radio left, and if it will remain under my exclusive control. Both are unlikely in my case so I will give such a radio a wide berth. However I would surely spruce up the cabinet, knobs etc and use the set as a decorational prop in my listening room!

Thanks

 

[captrajesh]

O.K. If you bring it to Bangalore I will give a try. In case the IF transformer or the coils are defective then it will become difficult. This can only be ascertained after checking.

Thats great news. How do se check the IF transformer and the coils? If they can be checked with multimeter, what should be the readings? It would be ideal to check these.at Hyd & then bring them to B'lore.

Edit:
Ashokji I think our posts crossed. Thank you for the clarification on behalf of Rajan ji; I guess you are right. Yes I wanted it purely for nostalgic reasons. I would want a working decorative piece.

 

[Pandu Rajan]

Dear Mr. Rajesh

I will have to check myself. The coils have got very low resistance.

Regards

P.Rajan

 

[aks07]

Dear Captain Rajesh

Good to see that that you have decided to proceed with restoration. The previous post was not to discourage you but to give a complete picture with this type of radio. I am glad that the heart is ruling mind in this case !

To make it safer you may install an isolation transformer. This need not be very large as the current draw is small. This can be in situ inside the cabinet. Since Rajan Sir has agreed to take this up, you may like to procure and send an isolation transformer as well. I know what kind of radios he fixes so its doubtful he will have an isolation tx at hand. Lets be safe during the repairs and after the radio is back to you

The IFT's have very fine windings that conduct high voltages. Usually IFT suffers mechanical damage to its core. This happens when non qualified mechanics fiddle with the adjustment screw. After many years these adjusters are jammed tight and applying excessive force just breaks the innards. There are ways to rewind and even repair the IFT but it is beyond the scope here.

All the best

AKS

 

[captrajesh]

I will have to check myself. The coils have got very low resistance.

I can understand. I'll have to visit Hyderabad to retrieve (yeah my mom would be reluctant to part with it even if it is for a while hyeahand personally lug it to Bangalore. I'll plan it soon.

To make it safer you may install an isolation transformer. This need not be very large as the current draw is small. This can be in situ inside the cabinet.

Ashok ji thank you very much for the encouragement. I can get one made here in Chennai. An EI core should do I guess. What would be the specs, I mean voltage at secondaries and also, the rating?

 

[aks07]

Dear Capt Rajesh

Best to seek Rajan Sir's advice as he is a retired Post Graduate in Electrical Engineering.

Something like this should be ok:

Primary 230VAC
Secondary 230VAC (0.6A).

Taking for about 10% loss this should run warm but not excessively hot. Don't oversize the TX as our primary aim is safety by limiting the amount of current that goes in. 100 to 130 VA is ok.

There should also be a 0.6A fast blow fuse and a 3 point cord with proper grounding.

Please take final approval from Rajan Sir.

Best regards

AKS

 

[Pandu Rajan]

Dear Mr. Rajesh

Mr Ashok is right. A 600ma (0.6A) , 230V/230V transformer will be more than sufficient. Kindly ensure that the stampings are of CRGO steel.

Edit:
I was going through the schematic of the Murphy radio model TUO777. The Filament voltage distribution is as follows.
1. UCH81- 19V,0.1A
2. UF89 - 12.6V,0.1A
3. UBC81- 14V,0.1A
4. UL84 - 45V,0.1A
5. UM84 - 19V,0.1A
6. UY85 - 38V,0.1A
7. Dial Lamp - 19V,0.097A
As per the schematic There is only one dial lamp. So the total voltage becomes 166.6V. All the filaments and the dial lamps are in series. To all these three additional resistance 300 Ohms+ 100Ohms + 250 Ohms are also connected in series. So the total voltage drop across these resistance comes to 65V. Thus total becomes 166V+65V = 230V. This is how the 230V is distributed. Also out of the three resistances one is adjustable type to correctly adjust the current to 0.1A which in turn adjusts the voltage correctly across each valve Filament.
The idea of giving the above details is the importance of the Dial Lamp. The voltage is 19V,0.097A. In case this dial lamp is fused the set will not work. I do not know whether now a days this bulb is available or not? It will be better if you can ensure whether the dial lamp is o.k. or not?

Regards

P.Rajan

 

[aks07]

The voltage is 19V,0.097A. In case this dial lamp is fused the set will not work.

Dear Sir

In case the bulb is fused, will it be ok to replace it with a 190R/3W resistor? It wont of course light up the dial.

Best regards
AKS

 

[reubensm]

Thats great news. How do se check the IF transformer and the coils? If they can be checked with multimeter, what should be the readings? It would be ideal to check these.at Hyd & then bring them to B'lore.

Edit:
Ashokji I think our posts crossed. Thank you for the clarification on behalf of Rajan ji; I guess you are right. Yes I wanted it purely for nostalgic reasons. I would want a working decorative piece.

Realistically you can check these for open circuit. Won't be able to get much or a impedence read as these are usually very low resistance. The SW antenna coils and all oscillator coils can be physically examined while the MW/LW antenna coil on the ferrite rod could be checked for open circuit. Usually these coils do not fail unless there is some physical damage or damage caused due to heat and ruthless technicians forcing the adjusting screws, in the case of the canned IFTs.

3. They are inherently unsafe. Today I would not like to have such a contraption around house that has the potential to kill someone. Back in the days one of our acquittance was fatally electrocuted when she accidentally touched the antenna wire in the roof.

As dramatic as this sounds (and this is true as I too have experienced these shocks as a kid), this is not likely in the modern context. To counter the danger, you can put in place the following:

1) Change the AC plug of the radio to a 3-way one. This will ensure that your mains cable polarity is maintained. However, do not change the mains cable to a 3-way one as if you ground the radio to your household electrical grounding, your radio is likely to pick up electrical inteference. Use a separate grounding for the radio external to your domestic electrical ground wiring

2) Use circuit breaker based switching in your domestic electrical circuit. This is your insurance policy. If you household circuit is old, then you can make a CB based plug point exclusively for your radio. Legrand CBs are a good bet, they are very reliable, but expensive.

 

[Pandu Rajan]

Dear Mr. Ashok

Yes we can replace the dial lamp by a 190 Ohm 3W resistance but the dial will not light up which is the real beauty of a valve set. Also 190 ohms may not be a standard value but series combination can be made. When 65 volt is dropped in the resistance lot of heat is generated. So increasing the resistance will increase the heat as 84 volt will have to be dropped. In earlier days in the smaller AC/DC radio sets the cabinet used to be of plastic and due to heat the cabinet used to get de-shaped.

Regarding the IFT resistances I will give a brief explanation here. Since I have been restoring Philips radios I know about the IFTs being used in these sets. These IFTs use very thin wire for winding sometimes even lower than 45 SWG. In the Philips IFTs the first IFT has a primary DC resistance of 9 ohm and the secondary is 5 ohm. In the 2nd IFT both the side the DC resistance is 5 Ohm. The winding is not done with one single wire but the coil is wound by taking 7 or 8 wires together and the coil is wound to get more no of turns. During restoring many radio sets I have found the resistance getting increased from 9 ohms to 18 ohms and 5 ohms increasing to 9 Ohms. This means that some of the wires (out of 7 or 8 ) of the coil are cut thereby increasing the resistance. This actually means the reduction of the total no of turns and resulting in lower gain. Higher the resistance lower will be the gain. If the wires have been snapped at the ends the IFT can be repaired but if it is in the middle it cannot be repaired and the IFT has to be replaced. So for a Philips radio I have the reference values and I can compare whether an IFT is O.K. or not. But in case of other makes and in the absence of reference values this becomes difficult.

Regards

P.Rajan

 

[aks07]

As dramatic as this sounds (and this is true as I too have experienced these shocks as a kid), this is not likely in the modern context. To counter the danger, you can put in place the following:

1) Change the AC plug of the radio to a 3-way one. This will ensure that your mains cable polarity is maintained. However, do not change the mains cable to a 3-way one as if you ground the radio to your household electrical grounding, your radio is likely to pick up electrical inteference. Use a separate grounding for the radio external to your domestic electrical ground wiring

2) Use circuit breaker based switching in your domestic electrical circuit. This is your insurance policy. If you household circuit is old, then you can make a CB based plug point exclusively for your radio. Legrand CBs are a good bet, they are very reliable, but expensive.

A fatal electrocution is certainly very dramatics. In this particular case the antenna wire had fallen on the clothesline. The lady went to spread out the laundry and zappp! Perhaps she went out without much drama Besides, a bit of sensationalism helps to drive home the point better and makes the new generation aware of the risk with this type of technology.

I am a stickler for safety both at works and home. When I build a tube gear, I ensure that it is safe today and in future when I am long gone. Idea is to make things as idiot proof as possible. It should be safe for someone say 50 years from now to poke around casually and still remain alive.

We cant guarantee that someone won't touch the chassis, or won't reverse wire the AC cord, or even change the polarity of wall plug fitting. There is no surety that the grub screw from the Knobs won't touch ones finger. Murphy's Law can strike any time. Just that a AC/DC radio will be less forgiving than a purely AC radio. Thus I feel AC/DC radios are unsafe by design.

Having said that probably millions of AC/DC sets were made without really killing as many people. But today our electrical equipments are required to meet high safety standard, and we (at least the new generation) tend to assume that even the old gear too is similarly safe. This assumption can be fatal.

I know I am sounding like a safety Nazi. Sometime even I cant believe just how much I have changed. For many years I had a hot-wired 845 amp running 1,500 VDC with exposed joints in our living room even as my daughter was a toddler. There were times when I would shoot down the road in a Triumph Twin 500cc bike at speed approaching 100 miles/hour. That too without any helmets or such. I shudder to think of that now. Several accident on the roads, too many HV zapps and now I realize how lucky it has been. I have come to respect safety.

Lets be safe first, foremost and last !

Since I have been restoring Philips radios I know about the IFTs being used in these sets

Do the Philips sets from 1930's too have 452,000 cycles as the IFT frequency?

Someone has offered to sell me a Philips radio that he claims was bought in in 1935 or so by his grandfather. There is no model marking left on the set. I have asked for pictures but that is proving to be beyond the capability of the current owner.

Since it is in another town i want to be sure about everything particularly the IFT's.

Best regards

AKS

 

[Pandu Rajan]

Dear Mr. Ashok

Most of the radio sets manufactured by Philips Had the IF frequency as 452KHz. I will have to checkup the radio sets manufactured between 1930 to 1940. The Philips radio sets manufactured in U.K. sometimes had a different I.F. frequency.
Even Mullard U.K. who were part of Philips Used 452Khz as the IF frequency.

I checked few sets between 1930 and 1936 where the IF frequency is 128Khz. So it is very difficult to say regarding the IF frequency of the older sets. One will have to check the particular model schematic/ service manual.

Regards

P.Rajan

 

[captrajesh]

Dial Lamp - 19V,0.097A

In case this dial lamp is fused the set will not work. I do not know whether now a days this bulb is available or not? It will be better if you can ensure whether the dial lamp is o.k. or not?

Thank you very much for the information sir. I'll check this out during my next visit to Hyd. I might as well scout for a lamp too. Even if one on the dial is working, this can remain as a spare.

Realistically you can check these for open circuit. Won't be able to get much or a impedance read as these are usually very low resistance. The SW antenna coils and all oscillator coils can be physically examined while the MW/LW antenna coil on the ferrite rod could be checked for open circuit. Usually these coils do not fail unless there is some physical damage or damage caused due to heat and ruthless technicians forcing the adjusting screws, in the case of the canned IFTs.

Thank you for the information Reuben; I'll check them as well.

Change the AC plug of the radio to a 3-way one.

Since the isolation transformer would help in fool-proofing the Radio from safety point of view, I might as get an iso trafo made.

Use circuit breaker based switching in your domestic electrical circuit.

I think my mom's house already has the CBs so no problem.

 

[nn_in]

Resources to troubleshoot All American Five Radio YouTube Channel The All-American Five Radio: Understanding and Restoring Transformerless Radios of the 1940'S, 50'S, and 60's: Richard McWhorter: 9781886606197: Amazon.com: Books

 

[shankar bhandarkar]

Dear Rajan
Did you check with BEL..... ore if you have valve numbers you can even try in mumbai
regards
bhandarkar

 

[reubensm]

A fatal electrocution is certainly very dramatics. In this particular case the antenna wire had fallen on the clothesline. The lady went to spread out the laundry and zappp!

in the modern context, this would not have happened as the circuit breaker in the house hold circuit would have tripped hyeah:

 

[Pandu Rajan]

Dear sir

Our body is safe if the current is within 30ma.In case it goes more than 30 ma it can be fatal. The amount of this current flowing through our body depends on various factors. Whether a person is wearing shoes or not? How good is the insulation of the shoes? How wet is the floor on which a person is standing? etc. So just having a circuit breaker is not sufficient Because in the market the minimum rating of the circuit breaker available is 2A.So unless an until you have a earth leakage circuit breaker which will trip if the leakage current exceeds 30ma all the other protections are of no use.

BEL do not have any valves because they have stopped manufacturing them long time back. BEL only manufactured 9 pin noval pin valves. My requirement is as follows:
1. EBL21
2. ECH21
3. EF22
4. EM4
5. EM34
6. AZ4
7. EM84
8. EL86

Except for sr. no 7 & 8 all the other valves were imported. EM84 and EL 86 were manufactured by BEL.

Regards

P.Rajan

 

[VenuEmages]

Hi,
I am in the process of restoring a Philips 15RB708-00S.
I need help with two issues.
1. Where do source the tuning dial strings in India? I could locate one in Illinois[USA]. I shall resort to that if it is not available in India.

2. Do you have a picture of the front panel?

regards

Venu

 

[reubensm]

Hi,
I am in the process of restoring a Philips 15RB708-00S.
I need help with two issues.
1. Where do source the tuning dial strings in India? I could locate one in Illinois[USA]. I shall resort to that if it is not available in India.

2. Do you have a picture of the front panel?

regards

Venu

Very recently, I bought a dial chord in a plastic packet from Rohini Electronics at Thakaraparambu for 10 bucks for fixing a Siemens Radio Dial. Your location says Trivandrum so I could not help smiling when you mentioned that you located one in Illinois :lol:

 

[Pandu Rajan]

Dear Mr. Venu

It is not very difficult to get the dial cord. Many radio shops still keep them. I am having the same. Do you happen to come to Bangalore? If you come to Bangalore I can give it to you. As regards the front panel - Do you want the photo of the dial only or the complete radio. I have posted a photo of the set in this thread some times back. If you want to have the photo of the Dial then I will have to send.

Regards

P.Rajan