1948 Magnavox "Berkley" Console Issues

[vortalexfan]

Hello everyone, earlier this year I picked up a 1948 Magnavox "Berkley" AM/SW/Phono Console (Chassis No. CR-198F) that still has its original Magnavox rebadged Webster-Chicago 2 Speed Record Changer in it (minus its original cartridge that was a flip-over variety that was flipped in a similar manner to the original Zenith "Cobra-Matic" Changers from the same time period where you flipped a lever mounted on the back of the tonearm to flip between the "LP" and "78" needle.)

In place of the original cartridge was a Sonotone 2T cartridge which was for some reason wired into the audio input jack for the optional FM Tuner accessory for this radio instead of the phono input jack and so I rewired the unit so the cartridge audio was inputted into the phono input jack again, but for some reason or another when I touch the wires going to the back of the cartridge I don't get any hum out of the unit when its switched to phono mode, but yet when I touch the phono input jack itself on the chassis I get a hum when I touch it, just not going through the wire going from the tonearm to the plug, and I have continuity between both ends of the "hot" and "ground" wires going from the cartridge wire to the plug going into the amplifier, but for some reason its not passing any electrical/audio signals through those aforementioned cables.

Any ideas as to what might be causing my no audio issue?

[Electronic M]

The original Zenith cobramatic changers did NOT have turnover cartridges. The first year models 1948 were 78 RPM only, and later models that had 33RPM had a single stylus that was a compromise tip size part way between LP and 78. The Zenith designed cobra pickup was originally a variable capacitance cartridge that FM modulated an oscillator tube that was demodulator for audio. None of these cartridges supported multiple styli. Zenith kept this scheme until the mid to late 50s then they switched to generic third-party ceramic turnover cartridges, but perplexingly kept using the cobramatic name and tone arm design for a while after the switch.

[vortalexfan]

Originally Posted by Electronic M

The original Zenith cobramatic changers did NOT have turnover cartridges. The first year models 1948 were 78 RPM only, and later models that had 33RPM had a single stylus that was a compromise tip size part way between LP and 78. The Zenith designed cobra pickup was originally a variable capacitance cartridge that FM modulated an oscillator tube that was demodulator for audio. None of these cartridges supported multiple styli. Zenith kept this scheme until the mid to late 50s then they switched to generic third-party ceramic turnover cartridges, but perplexingly kept using the cobramatic name and tone arm design for a while after the switch.

OK, my bad, I was thinking that because I have an old Zenith S-9011 Record Player from the early 1950s that has a two tip needle arrangement that you have to "flip" the needle (its actually more of a cantilever) by pressing the back of the tone arm which allows the needle to switch between an LP or 78 Needle, and that record player is called a "Cobra-Matic".

Anyways that doesn't answer my question as to why the original factory phono input hookup on the back of this radio is not responding to any "electrical signals" being injected into the audio cable but will respond to "electrical signals" being injected directly into the phono input itself minus the audio cables.

[old_tv_nut]

Did you check your cable for a short between signal and ground?

[vortalexfan]

Originally Posted by old_tv_nut

Did you check your cable for a short between signal and ground?

No I didn't. How might I do something like that?

Also the wire I'm using is a wire that someone jury-rigged at one point in time when they replaced the original catridge with a Sonotone 2T Cartridge.

Can I assume that the cartridge ground on the record player on this unit is supposed to be grounded off onto the record player chassis or is it supposed to "float" and then get grounded at the radio chassis?

[old_tv_nut]

To check for signal to ground short in a cable, disconnect the cable from the equipment and then connect one ohmmeter lead to the signal (center conductor) and the other ohmmeter lead to the ground (outer conductor/shield).

Regarding grounding, your turntable should have its own ground wire to connect to the ground terminal on the amplifier.

I don't know what to tell you about your "jury rigged" cartridge wire, but I think if you have the correct wire the cartridge and cartridge shell should float and only be grounded via the connector at the amplifier. It's been a looong time since I wired up my turtable, but I think there is no way provided to connect the cartridge wire to the turntable chassis.
I hope somebody else chimes in here.

[old_tv_nut]

I just looked at the back of my receiver (with a flashlight and a mirror) and it appears I do not have a separate ground wire. Now I don't know if the turntable has one or not, or if it could be disconnected because it made things worse, so, again I hope someone else chimes in.

[nasadowsk]

Originally Posted by Electronic M

The original Zenith cobramatic changers did NOT have turnover cartridges. The first year models 1948 were 78 RPM only, and later models that had 33RPM had a single stylus that was a compromise tip size part way between LP and 78. The Zenith designed cobra pickup was originally a variable capacitance cartridge that FM modulated an oscillator tube that was demodulator for audio. None of these cartridges supported multiple styli. Zenith kept this scheme until the mid to late 50s then they switched to generic third-party ceramic turnover cartridges, but perplexingly kept using the cobramatic name and tone arm design for a while after the switch.

Wurlitzer used cobras for a few years. Far longer than they should have. Seeburg and AMI had far far better sound systems that blew the Cobra out of the water. Wurlitzer finally dimped cobra when stereo came around…

[vortalexfan]

I got it fixed, it was a short in the wiring from the tonearm to the amplifier, apparently the way I had it wired up was that the "ground lead" of the headwire was tied to the chassis of the turntable which was causing a short, so I wired it so that the ground was floating separate from the turntable chassis and now its working fine.

Unfortunately the cartridge (a Sonotone 2T) is nearly dead because its not putting out much audio (the volume has to be cranked up to the halfway point to even hear anything) which means I'm going to have to find another mono (Hi-Fi) 1/2" mount flip-over cartridge to use with this record player.

Any suggestions as to a good replacement cartridge to use with this record player?

[vortalexfan]

Update: I picked up on the cheap (I was the only bidder) on feebay a lot of 30 record player serviceman items (including several cartridges, needles, a needle tracking weight scale, tonearm wire, cartridge mounting screws and spacers, a desoldering bulb etc.) for $9.99 plus shipping and one of the cartridges in the lot happened to be a NOS Sonotone 2T Cartridge so I should be good to go to get this unit fixed up the rest of the way!

[vortalexfan]

OK so I have a quick question, this radio uses 2 6L6Gs in push-pull configuration for about 45 watts or so and when I got this unit it had its original matched set of Ken-Rad 6L6G tubes in it but one of the tubes was microphonic and I happened to have a Conn Rebadged GE 6L6GC tube that I salvaged from an old Conn Organ Amplifier to sub in to confirm my suspicions about one of the original 6L6G tubes being microphonic.

I know with push-pull amplifiers it is best to replace tubes in pairs but unfortunately 6L6G tubes (NOS) are $40 a pop and 6L6GC tubes are $80 a pop, and I have a whole ton of 6V6 tubes laying around including a matched set of Zenith (Sylvania) 6V6G tubes that I salvaged from a Zenith 10S690 Console that I parted out.

I was wondering if I could use those 6V6G tubes in this Magnavox Console in place of the 6L6G tubes since the 6V6 tubes are more readily available and cheaper than the 6L6 tubes?

[Electronic M]

6V6 have a lower power rating than 6L6. You can plug 6V6s in for temporary testing purposes, but depending on bias and the volume you run it at they will deliver less output power and or fail prematurely.

Here's a tip a 6BG6 is a 6L6 with the plate run out the top cap, and an 807 is a fat pin 6BG6. They can be adapted and will work fine.

[DavGoodlin]

I have a Magnavox Berkeley 134 and bought two JJ Tesla 6L6 when these were less $$. The original Ken Rad 6L6G seem to be OK, so the JJ's made little difference.
Matching tubes is necessary if closer to design limits, but Magnavox is usually tame enough on two good tubes, so this is a non-issue.
This amp is rated for 20 watts in Magnavox CR198 here http://www.nostalgiaair.org/PagesByM...5/M0010335.pdf

But 1947 sales literature I for the Berkeley stated 15 watts from the two speakers. Looking at Antique Electronic Supply website, a 5881 will work, listed for $26.

RCA or Ken Rad (GE) metal versions of 6L6, of which my 1948 Windsor has four, is rated 45 watts. These are more reasonably priced. https://www.ebay.com/itm/35423726914...Bk9SR-DLz7fbYA

[old_coot88]

Originally Posted by Electronic M

Here's a tip a 6BG6 is a 6L6 with the plate run out the top cap, and an 807 is a fat pin 6BG6. They can be adapted and will work fine.

I've direct-swapped 6BQ6 and 'DQ6 for 6L6's. Basing's the same except for the plate. Just gotta run a wire up from pin 3 to the top cap.

[maxhifi]

Ask nicely for a set of used 6L6s from a guitar player. They'll be useful in a radio for years after they're too weak to sound their best in a guitar amp. Or use metal 6L6 tubes, they're still cheap.