Unknown model Farnsworth AA6 tube lineup

[C.Copperpot]

I bought this late 1940's Farnsworth radio for $5 this weekend. The
model number label is missing from the bottom. It's a table model. AM
only. It seems they had a few variations that used this case. The tube
lineup that is in the radio is 12SK7, 12SA7, 12SK7, 12SQ7, 50L6, 35Z5
That adds up to 130. Looking at schematics on Nostalgia Air, other
variations have used two 6SS7 tubes instead of the 12SK7's. Another
schematic uses the 12SK7's but uses a 35L6 instead of the 50L6. Does
it matter or should I change the 50L6 for a 35L6? Or I could change
the two 12SK7's for 6SS7's?

[Hank]

Post by C.Copperpot
I bought this late 1940's Farnsworth radio for $5 this weekend. The
model number label is missing from the bottom. It's a table model. AM
only. It seems they had a few variations that used this case. The tube
lineup that is in the radio is 12SK7, 12SA7, 12SK7, 12SQ7, 50L6, 35Z5
That adds up to 130. Looking at schematics on Nostalgia Air, other
variations have used two 6SS7 tubes instead of the 12SK7's. Another
schematic uses the 12SK7's but uses a 35L6 instead of the 50L6. Does
it matter or should I change the 50L6 for a 35L6? Or I could change
the two 12SK7's for 6SS7's?

Hard to tell. Farnsworth ET-064 used 6SS7's/50L6 and GT-064 used
12SK7's and 35L6. Schematics look identical.

Take a look at the brand names and date codes on the tubes, and see if
most of them match. If so, I'd use a 35L6, if you want to change it.
Actually, I'll guess that the set will play perfectly well with the
50L6, just be a bit slow to warm up. That assumes your mains voltage is
120 volts, which is the US standard nominal most places (and has been
for some time).

Hank

[C.Copperpot]

On Tue, 14 Nov 2017 07:32:36 -0000 (UTC),

Post by Hank

Post by C.Copperpot
I bought this late 1940's Farnsworth radio for $5 this weekend. The
model number label is missing from the bottom. It's a table model. AM
only. It seems they had a few variations that used this case. The tube
lineup that is in the radio is 12SK7, 12SA7, 12SK7, 12SQ7, 50L6, 35Z5
That adds up to 130. Looking at schematics on Nostalgia Air, other
variations have used two 6SS7 tubes instead of the 12SK7's. Another
schematic uses the 12SK7's but uses a 35L6 instead of the 50L6. Does
it matter or should I change the 50L6 for a 35L6? Or I could change
the two 12SK7's for 6SS7's?

Hard to tell. Farnsworth ET-064 used 6SS7's/50L6 and GT-064 used
12SK7's and 35L6. Schematics look identical.
Take a look at the brand names and date codes on the tubes, and see if
most of them match. If so, I'd use a 35L6, if you want to change it.
Actually, I'll guess that the set will play perfectly well with the
50L6, just be a bit slow to warm up. That assumes your mains voltage is
120 volts, which is the US standard nominal most places (and has been
for some time).
Hank

Thank you Hank.
I think the set may have originally had Kenrad tubes in it. What's
throwing me off is one 12SK7 is a metal Kenrad and the other is an RCA
12SK7GT. The 50L6 is a Sylvania.

[Peter Wieck]

Post by C.Copperpot
I bought this late 1940's Farnsworth radio for $5 this weekend. The
model number label is missing from the bottom. It's a table model. AM
only. It seems they had a few variations that used this case. The tube
lineup that is in the radio is 12SK7, 12SA7, 12SK7, 12SQ7, 50L6, 35Z5
That adds up to 130. Looking at schematics on Nostalgia Air, other
variations have used two 6SS7 tubes instead of the 12SK7's. Another
schematic uses the 12SK7's but uses a 35L6 instead of the 50L6. Does
it matter or should I change the 50L6 for a 35L6? Or I could change
the two 12SK7's for 6SS7's?

a) Does it work.
b) What does it say on the nameplate (XX watts @ YYY Volts AC/DC).
c) Then measure the voltage at your wallplate.

Point being that these days, finding 125 - 130 VAC at the wallplate is not unusual. So, 'starving' your filaments may not be actually starving them at all. Further to this, filaments run at a lower voltage - as long as they work - last far longer than at a higher voltage than nominal.

Just keep that in mind before making any changes.

Peter Wieck
Melrose Park, PA

[C.Copperpot]

Post by Peter Wieck
a) Does it work.
c) Then measure the voltage at your wallplate.
Point being that these days, finding 125 - 130 VAC at the wallplate is not unusual. So, 'starving' your filaments may not be actually starving them at all. Further to this, filaments run at a lower voltage - as long as they work - last far longer than at a higher voltage than nominal.
Just keep that in mind before making any changes.
Peter Wieck
Melrose Park, PA

Thanks Peter
I have to do a re-cap before "firing" it up but I can see under the
chassis that one of the wax caps had a meltdown/exploded.
There is no info tag on the radio.
My line voltage runs around 123 - 125 VAC

[Terry S]

Post by C.Copperpot
I bought this late 1940's Farnsworth radio for $5 this weekend. The
model number label is missing from the bottom. It's a table model. AM
only. It seems they had a few variations that used this case. The tube
lineup that is in the radio is 12SK7, 12SA7, 12SK7, 12SQ7, 50L6, 35Z5
That adds up to 130. Looking at schematics on Nostalgia Air, other
variations have used two 6SS7 tubes instead of the 12SK7's. Another
schematic uses the 12SK7's but uses a 35L6 instead of the 50L6. Does
it matter or should I change the 50L6 for a 35L6? Or I could change
the two 12SK7's for 6SS7's?

Very common to see the 50L6 subbed for the 35L6, or other 50V tubes subbed for their 35V counterparts in AA5s and AA6s. Remember the original line voltage was 110V while the grid was growing. My typical home line voltage on a non-AC day is 127V, and I've seen 131V. The lowest I've ever measured is 122V. If the set works, leave it alone. If it doesn't, figure out why before changing to a 35V tube.

A couple days last summer, the local utility had some "issues" and the line voltage on one phase at my work was 180V. The other phase was 30V. Needless to say we lost a bunch of equipment, including some very expensive closed circuit video gear designed to work in the EMC chamber. Immune to high RF fields, but apparently not immune to high line voltage.

[C.Copperpot]

On Tue, 14 Nov 2017 04:47:57 -0800 (PST), Terry S

Post by Terry S
Very common to see the 50L6 subbed for the 35L6, or other 50V tubes subbed for their 35V counterparts in AA5s and AA6s. Remember the original line voltage was 110V while the grid was growing. My typical home line voltage on a non-AC day is 127V, and I've seen 131V. The lowest I've ever measured is 122V. If the set works, leave it alone. If it doesn't, figure out why before changing to a 35V tube.
A couple days last summer, the local utility had some "issues" and the line voltage on one phase at my work was 180V. The other phase was 30V. Needless to say we lost a bunch of equipment, including some very expensive closed circuit video gear designed to work in the EMC chamber. Immune to high RF fields, but apparently not immune to high line voltage.

Thanks Terry
So from the replies, I guess my plan will be to re-cap and leave the
tube lineup as it is for now. If it starts up too slow, I'll try a
35L6.

[h***@gmail.com]

Post by C.Copperpot
On Tue, 14 Nov 2017 04:47:57 -0800 (PST), Terry S

Post by Terry S
Very common to see the 50L6 subbed for the 35L6, or other 50V

tubes subbed for their 35V counterparts in AA5s and AA6s.
Remember the original line voltage was 110V while the grid
was growing. My typical home line voltage on a non-AC day is 127V,
and I've seen 131V. The lowest I've ever measured is 122V.
If the set works, leave it alone. If it doesn't, figure out
why before changing to a 35V tube.

You can (carefully) measure the voltage on each when it is on.

You can also use a Variac (tm) to bring the voltage up slowly,
and then measure them, if you suspect any might be wrong.

Note also, that if the filaments don't heat at the same rate,
the voltage will be higher on some. If you really want it to
last, always bring them up slowly.

[C.Copperpot]

On Tue, 14 Nov 2017 06:35:15 -0800, C.Copperpot

Post by C.Copperpot
On Tue, 14 Nov 2017 04:47:57 -0800 (PST), Terry S

Post by Terry S
Very common to see the 50L6 subbed for the 35L6, or other 50V tubes subbed for their 35V counterparts in AA5s and AA6s. Remember the original line voltage was 110V while the grid was growing. My typical home line voltage on a non-AC day is 127V, and I've seen 131V. The lowest I've ever measured is 122V. If the set works, leave it alone. If it doesn't, figure out why before changing to a 35V tube.
A couple days last summer, the local utility had some "issues" and the line voltage on one phase at my work was 180V. The other phase was 30V. Needless to say we lost a bunch of equipment, including some very expensive closed circuit video gear designed to work in the EMC chamber. Immune to high RF fields, but apparently not immune to high line voltage.

Thanks Terry
So from the replies, I guess my plan will be to re-cap and leave the
tube lineup as it is for now. If it starts up too slow, I'll try a
35L6.

Just an update - I recapped and changed a 150 ohm resistor that was
reading 335 ohms. I re-wired the power switch with the hot lead. The
chassis had over 80v on it with the power off. It sounds pretty good.
It starts up a little slow because of the 50L6 instead of a 35L6 but
I'm going to leave it in there. This model has the dial light attached
to the pointer which is pretty cool.

[Peter Wieck]

Post by C.Copperpot
Just an update - I recapped and changed a 150 ohm resistor that was
reading 335 ohms. I re-wired the power switch with the hot lead. The
chassis had over 80v on it with the power off. It sounds pretty good.
It starts up a little slow because of the 50L6 instead of a 35L6 but
I'm going to leave it in there. This model has the dial light attached
to the pointer which is pretty cool.

An altogether good outcome. Less stress on the tubes, and a working radio.

As a general thought, it might be a good idea to stock up on 50L6 tubes and/or similar up-voltage tubes depending on what one has at the wallplate typically. Most especially if one actually plays the radios in the collection.

Peter Wieck
Melrose Park, PA

[C.Copperpot]

I guess I'll call it Model GT-60
That one uses the 12SK7 tubes.