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 HMV 661 console radio electros
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 Return to top of page · Post #: 1 · Written at 9:16:55 PM on 17 January 2020.
Normf's Gravatar
 Location: Erowal Bay, NSW
 Member since 19 June 2018
 Member #: 2256
 Postcount: 85

Finally getting to work on this radio.
The circuit shows the two filter caps with C34 going to ct of secondary of transformer and refers to it as regulating type electrolytic.
Can someone tell me what type of electro it is referring to, can I use a normal 600v 16μF electro here same as the other electro?
Thanks


 
 Return to top of page · Post #: 2 · Written at 9:59:00 PM on 17 January 2020.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5342

They were wet electros which "featured" high leakage current and I gather were a bit of a gimmick for a while in that era:

QUOTE: The leakage current characteristics of wet electrolytic capacitors are such that when a potential is applied which exceeds the value of the initial formation voltage of the anodic film a sharp increase in leakage current values is obtained. Advantage of this characteristic is taken in the design of a type of capacitor termed the regulating or self regulating type. The normal increase in leakage current with application of potentials in excess of formation voltages can be still further increased by two methods. In other words, the regulation can be increased; first, through the use of a low value of voltage of anodic film formation in connection with the use of a relatively high resistance electrolyte and second, through the use of a low voltage of anodic film formation with the use of a relatively low resistance electrolyte.

It is, however, general practice to rate regulating capacitors at an operating voltage at or slightly above the potential used in initially forming the anodic film. It is also common practice to specify the degree of regulation by specifying a maximum leakage current at the rated operating voltage and a minimum value of leakage current at a higher value of voltage termed the regulating voltage. Usually the regulating voltage specified is 75 volts more than the rated operating voltage. The magnitude of increase in leakage current varies somewhat with the capacity and general type of capacitor.


http://www.tuks.nl/Mirror/faradnet_com/deeley/chapt_06.htm#regchar

Advice is to replace them (and neighbouring electros) with higher voltage caps.


 
 Return to top of page · Post #: 3 · Written at 10:07:34 PM on 17 January 2020.
Normf's Gravatar
 Location: Erowal Bay, NSW
 Member since 19 June 2018
 Member #: 2256
 Postcount: 85

Thanks GTC
The manual states 428 volts at input to filter and 275 at output of filter, so 600v caps would be OK to use here.


 
 Return to top of page · Post #: 4 · Written at 1:33:19 PM on 18 January 2020.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1349

Those electros give new meaning to "steam powered radio"!

Sounds like a truly bad idea!

Obviously it didn't catch on.....


 
 Return to top of page · Post #: 5 · Written at 11:23:41 PM on 18 January 2020.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3865

The AORSM circuit says 550 Peak volts for the first filter cap but I used 600V caps. The start up voltage with 5Y3 can go to twice running volts. I did re-draw (AutoCAD) all of the boards. The one I worked on was the modified one that has EBF2G. That has circuit changes to accommodate that valve, apparently WD scarpered off with all the 6B8's mid 1941. 6K7 was unusual as well, nearly all Australian radios used 6U7 (aka 6D6 & 58 with heater & base changes).

The capacitance of the first cap in a capacitor input filter is significant: The lower it is the lesser is the voltage developed & it is never unusual with sets with very high voltages to use choke input filter to take the stress off of the rectifier.

Its electrolytic caps were mounted on the speaker: I used two Tag strips & mounted them on the inside of the chassis. Beware of the negatives the field id in "B-" not "B+" and the set is back biased. All sorts of traps in that one.

Marc


 
 Return to top of page · Post #: 6 · Written at 11:43:45 PM on 18 January 2020.
Normf's Gravatar
 Location: Erowal Bay, NSW
 Member since 19 June 2018
 Member #: 2256
 Postcount: 85

Thanks Marc
Could I get a copy of your redraw of the boards.
Did you use 16μF 600v caps as first and second filter as per circuit?
As the speaker is damaged was wondering about using the field coil from the speaker as the filter choke and using
a PM speaker to replace it.

Norm


 
 Return to top of page · Post #: 7 · Written at 10:58:36 AM on 19 January 2020.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3865

The circuit calls for a lesser value for the second, however the starting surge affects all & I prefer the same. It also comes down to inventory: Stocks cost money.

Contrary to the beliefs of some one replaces every electrolytic & RB types with wires left long (heat) can be mounted on the socket.

You can use the field, but if you remove it from the speaker, mount it with a steel plate under it.

If you send email (don't think mines hidden) I can send.

Marc


 
 Return to top of page · Post #: 8 · Written at 2:06:05 PM on 19 January 2020.
Normf's Gravatar
 Location: Erowal Bay, NSW
 Member since 19 June 2018
 Member #: 2256
 Postcount: 85

Thanks Marc
I have unhidden my email address.


 
 Return to top of page · Post #: 9 · Written at 5:26:48 PM on 19 January 2020.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3865

Documents sent 17:26


 
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