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 Post subject: Wards WG&C series 13a35
PostPosted: Apr Sat 06, 2019 4:36 am 
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Joined: Aug Sat 16, 2008 10:42 pm
Posts: 169
Working on this all tube chassis out of a wards console. Everything built on one giant slab with single ended 6bq5s and bizarro dual output xfmr setup to derive a center bass "channel" for the big woofer while mids and tweets provide true stereo from the VM changer. The sticker on the side has been defaced and only a partial number is visible. But somehow the schematic is present with the numbers shown above on it.
It sort of works with all original parts from 1961 maybe; I say that due to presence of the am-fm simul setup on the selector so you can hear left from AM and right from FM. This is just before the 1962 adoption of encoded MPX FM we have today. Of course I will put in new filters and coupling but for now, here is the mystery:
In the FM tuner is a 6GY8 which is not in my RCA manual but has three triodes. The schematic from wards calls for a 6AQ8 which is a dual triode; both on 9 pin mini base. These tubes are not substitutes in any book I have and the FM is tuning but poorly. The oscillator is on freq and so is the IF but the signal is weak and distorted. What I am wondering is if anyone has old schematics for wards console tuners that show either of these tubes as the sole occupant of the front end. I am reluctant to acquire a 6AQ8 and put it in here for fear it will blow the tuner out completely since the pinout is wildly different. The question is: what would you do in this situation? Both tubes are pricey and I cannot afford to destroy one.

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 Post subject: Re: Wards WG&C series 13a35
PostPosted: Apr Sat 06, 2019 11:23 am 
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Joined: Jul Mon 26, 2010 8:30 pm
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Location: Annapolis, MD
Assuming that the wiring has not been modified, install the correct tube.

One of the first things to do in a restoration is to look for any signs of damage, overheating, or prior modifications. If there is any evidence of past "meddling", then check everything against the schematic.

Brief Googling found no evidence that a 6GY8 could be subbed for a 6AQ8, even with circuit modifications. It does appear that both are appropriate for an FM front end.

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"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Wards WG&C series 13a35
PostPosted: Apr Sat 06, 2019 5:30 pm 
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Joined: Aug Sat 16, 2008 10:42 pm
Posts: 169
Mark thank you for affirming my intuition that the 6gy8 maybe does belong in this unit. I checked for B+ on the pins with tube out and sure enough it is found on what would be the plates of a 6gy8, not the plates of a 6ay8. As mentioned initially, the set does tune though not strongly. Once the power supply is rebuilt, things might improve. --TH

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 Post subject: Re: Wards WG&C series 13a35
PostPosted: Apr Sat 06, 2019 6:51 pm 
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Location: Annapolis, MD
Can you post a link to the schematic you're using?....I can't find anything close to that model number under airline, wells gardner, etc.

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"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Wards WG&C series 13a35
PostPosted: Apr Sat 06, 2019 7:53 pm 
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Joined: Aug Sat 16, 2008 10:42 pm
Posts: 169
All I have is a piece of paper and here it is photographed just now.


Attachments:
20190406_114544 wards 1 shrunk.jpg
20190406_114544 wards 1 shrunk.jpg [ 120.74 KiB | Viewed 185 times ]
20190406_114610 wards 2 shrunk.jpg
20190406_114610 wards 2 shrunk.jpg [ 120.31 KiB | Viewed 185 times ]

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