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 Post subject: Help w/ West H-122 conversion
PostPosted: Jun Wed 14, 2017 3:47 am 
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Location: Vancouver Island, Canada
I recently acquired this Canadian Westinghouse RA607, AKA H-122.
The crack in the cabinet makes it nearly worthless as a collectible, but I like the bigger than average speaker with push-pull octal output tubes.
What I don't like is the series resistor and 6 tubes drawing 0.3 amps. So my plan for the winter months is to
1) replace the rectifier with a silicon diode, 2) add a 6 volt filament transformer, and
3) replace the 25L6's with 6V6's.
Another small isolation transformer will provide B+.

So looking at the schematic, the bias circuit for the 25L6 output tubes is not clear to me. My way of installing 6V6 output would be to dig up a schematic with typical cathode biasing and copy that. Any suggestions?

Nothing I do under the chassis will do this radio any lasting harm, if that bothers anyone. My new schematic diagram will go in but will leave the original untouched.
The transformers will probably go in a narrow box under the radio, keeping the small footprint.
Maybe an addition to the rear could act as a speaker enclosure for improved bass, again with no harm done.

Does anyone have a suggestion for wiring improvements?


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 Post subject: Re: Help w/ West H-122 conversion
PostPosted: Jun Wed 14, 2017 3:33 pm 
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You could use 6V6's but they operate better with higher B+ voltage. Why not use 6W6 as these are about the same as 25L6 but have a 6 volt filament.

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 Post subject: Re: Help w/ West H-122 conversion
PostPosted: Jun Wed 14, 2017 4:25 pm 
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Joined: Dec Sat 24, 2011 9:17 pm
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Location: Vancouver Island, Canada
Thanks, I see your point. I see I can get 6W6GT's for $3 each.

However, the heater current draw is considerably more at 1.2 amps. My filament transformer has a max output of 3 amps. With the 3 tubes in the front end drawing 0.3 amps each, I think I'd get into trouble there.

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 Post subject: Re: Help w/ West H-122 conversion
PostPosted: Jun Thu 15, 2017 3:44 pm 
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Joined: Dec Sat 24, 2011 9:17 pm
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Location: Vancouver Island, Canada
I've scoured the 1973 characteristics tables and didn't find any better power tubes to use.
I need to keep the B+ in the 100 volt range or this will just not work. My goal is simply to eliminate the big resistor and isolate the B+.

So will now go thru my boxes of small power transformers.

If I find a 25 or 50 volt PT, I can stay with the existing tube string, powered by 3 little transformers. 8)
Or a second 6.3 v transformer could be used with the 6W6's.

Another possibility would be to use 50L6's in series with maybe a 12 volt rectifier.

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 Post subject: Re: Help w/ West H-122 conversion
PostPosted: Jun Sun 18, 2017 12:05 am 
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Joined: Dec Sat 24, 2011 9:17 pm
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Location: Vancouver Island, Canada
Ok I think I have it now. I found a 24 volt doorbell transformer in my boxes of stuff.
It is rated at 20 volt amps, so dividing 20 by 24 volts I get 0.8 amps, plenty to supply the heaters of two 25L6 tubes.
The 6.3 volt transformer can supply the 6 volt tubes, and the isolation transformer gives me 120 volts for the B+. No need to alter anything else in the original circuit.
The radio will be perched on top of a narrow box, open at the back, containing the three transformers.
Hope it works. :lol:


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trans3.jpg
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 Post subject: Re: Help w/ West H-122 conversion
PostPosted: Jun Sun 18, 2017 12:32 am 
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Too bad you didn't find the console that went with that radio , the head slipped into the record player cabinet , my parents and grandparents both had the radio record player version of the radio .

Just changing output tubes won't improve , the sound quality , a better output transfomer would be needed , also the IF band width will limit the AM sound fidelity .

I still have the blonde version of that radio that belong to my parents .

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 Post subject: Re: Help w/ West H-122 conversion
PostPosted: Jun Mon 19, 2017 12:53 am 
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Location: Vancouver Island, Canada
Yes, that blond console is a striking unit if it is like the one on the Radioattic site.
There was a table phono version as well, but I have limited space and no 78"s to play, so I like the small footprint of the head alone.
It is a versatile design, but maybe didn't sell as well as they hoped?

I have 2 AM stations I tune to sometimes, but mostly stream audio from some other source. That is why I want to isolate the chassis with my transformer add-on.

I am just digging into the chassis now, in my temporary work station. I've clamped on two short planks for a stand.
The multi-cap has 2 blacks out either end. 2 go to tubes so are positive ends. 2 wires go to a terminal strip but only one goes from there to the B- spider web, so that point on the terminal strip is the anchor for my new caps.

The big resistor tests good, so I'll be able to get the set working good before moving on with modifications to the power supply.


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WestEcaps2.jpg
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 Post subject: Re: Help w/ West H-122 conversion
PostPosted: Jun Mon 19, 2017 1:09 am 
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Your work might be simplified if you just used an isolation transformer , if you have two like transfomers in your collection of parts and connect the low voltage winding together to get an isolation transfomer .

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 Post subject: Re: Help w/ West H-122 conversion
PostPosted: Jun Mon 19, 2017 2:09 am 
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Joined: Dec Sat 24, 2011 9:17 pm
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Location: Vancouver Island, Canada
Yes, if the ballast resistor proves to be satisfactory, I may leaves all as is. The heat will keep my desk warm.

Something different with my Canadian R-603 is that a 16 mfd E cap goes to pin 4 screen grid of the 6SA7. There is also a 0.5 mfd wax cap doing the same thing, B- to pin 4. The 2 paralleled caps can be seen in the H-122 schematic, directly above the heater string in the picture. The small unpolarized cap performs a slightly different duty than the large polarized cap, so I will stick with the diagram and existing wiring.

In the H-122, there is only the .05 cap, or am I missing something?

http://www.nostalgiaair.org/Resources/095/M0024095.htm

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Last edited by westcoastjohn on Jun Mon 19, 2017 2:56 am, edited 1 time in total.

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 Post subject: Re: Help w/ West H-122 conversion
PostPosted: Jun Mon 19, 2017 2:25 am 
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The two caps in parallel is not unusual , it might have been made to work on 25HZ , and needed the extra filtering

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 Post subject: Re: Help w/ West H-122 conversion
PostPosted: Jun Mon 19, 2017 3:03 am 
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Location: Vancouver Island, Canada
Yes, this radio can operate on 25 or 60 cycles.

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 Post subject: Re: Help w/ West H-122 conversion
PostPosted: Jun Mon 19, 2017 3:39 am 
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If the radio runs too hot sub in a 35Z6 in place of the 25Z6 and that will drop 10 more volts , if a 50Z6GT was to be used you could change the ballast resistor to 12 ohm 10 watts for the pilot lamp voltage source .And would give it about 124 volt voltage drop which with today's line voltage would be about right .

http://frank.pocnet.net/sheets/127/3/35Z6G.pdf

http://frank.pocnet.net/sheets/021/2/25Z6.pdf

http://frank.pocnet.net/sheets/201/5/50Z6G.pdf

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 Post subject: Re: Help w/ West H-122 conversion
PostPosted: Jun Mon 19, 2017 10:46 pm 
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I have installed a cluster of new caps, applied power, and found that my 25Z6 has an open filament.
The good part is that most likely the rest of the tubes were doing their job prior to that event.
They all show a good heater filament to the DMM.

So I need a rectifier tube, anyway. But was actually searching for a silicon one to tack in. :oops:
The heater of a 25L6 has a resistance of 11.7 ohms, which drops 25 volts. So a diode and a 16 ohm resistor will sub for the bad rectifier, somebody slap me if I'm wrong. :lol:

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 Post subject: Re: Help w/ West H-122 conversion
PostPosted: Jun Tue 20, 2017 2:12 am 
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You would need a second resistor the same value as the ballast resistor , and a .250 ma fuse to replace the 25Z6 . A tube's filament resistance cold is lower than its resistance hot so measuring it cold won't give you the correct value .

Was the 25Z6 good before you replaced the parts , if so very possible you now have a B+ short .

The ballast resistor could short to the chassis the way it is made , and they like to go bad ,candohm resistors famous for going bad , it is metal and riveted to the chassis the fish baper cumbles wit age and can open and or short to the chassis .

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 Post subject: Re: Help w/ West H-122 conversion
PostPosted: Jun Tue 20, 2017 3:22 am 
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Joined: Dec Sat 24, 2011 9:17 pm
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Location: Vancouver Island, Canada
This radio came to me not working. First time I applied power was yesterday, no heaters, found the recifier was bad.
I can't use a 35Z5 as this tube string draws 0.30 amps.
The resistor seems to be isolated from the chassis, but I know what you are saying. Also I don't know if a short circuit took the rectifier out or if it just expired.

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 Post subject: Re: Help w/ West H-122 conversion
PostPosted: Jun Tue 20, 2017 3:52 am 
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A 35Z6 would be a drop in replacement , to replace the 25Z6 with today's higher line voltages .


https://docs.google.com/spreadsheets/d/ ... 0foD#gid=4

a 35Z6 is $5 for a new one and $2.50 for a used one + shiping .

http://frank.pocnet.net/sheets/127/5/50Y6GT.pdf this would be a good choice and get rid of the ballast resistor

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 Post subject: Re: Help w/ West H-122 conversion
PostPosted: Jun Wed 21, 2017 1:16 am 
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Location: Vancouver Island, Canada
Thanks for pointing out my goof in the resistor requirement.

Your suggestion of a 50Z6 with a 12 ohm resistor for the pilot lamp makes sense.

http://tubedata.jp/sheets/201/5/50Z6G.pdf

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