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 Post subject: Help with Freshman Masterpiece
PostPosted: Sep Wed 01, 2021 9:36 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 7784
Location: Toledo, Ohio
I have a model 6F-5 that all I get out of the built-in speaker or external horn speaker is a faint sort of motorboating. If I use headphones I get a very low audio that is understandable. Right now I have a CX-112 tube as the output tube but I have also tried using a 01A with the same result.

The first interstage transformer had an open primary so I replaced it with a solid state replacement that someone here on ARF was selling some time ago. The second interstage transformer ohms out on both windings so I left it in place.

I checked the condition of the capacitors and they tested almost spot on as far as value goes but the adjustable grid leak resistor was open. I have been subbing in different values of resistors staring with 1M with no luck. Any ideas as to what might be the issue with the crappy audio from the final stage?

The following is the closest schematic I could find to represent this model except that the internal speaker connection is actually parallel to the horn jack so when you plug in the horn the internal speaker is never disconnected.

Attachment:
freshmansch-1.jpg
freshmansch-1.jpg [ 417.78 KiB | Viewed 895 times ]

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Last edited by Jim Dutridge on Sep Thu 02, 2021 12:00 am, edited 1 time in total.

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 Post subject: Re: Help with Freshman Masterpiece
PostPosted: Sep Wed 01, 2021 11:09 pm 
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Joined: May Sat 30, 2015 11:49 pm
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Location: Keystone Heights, FL, USA 32656
Maybe verify that you have 90 volts on the plate of both RF tubes and both AF tubes. 22 or 45 volts on detector plate.

What are the resistance values of the 2nd transformer, rather then “ohms out”?

Solid state sub connected correctly?

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 Post subject: Re: Help with Freshman Masterpiece
PostPosted: Sep Wed 01, 2021 11:36 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 7784
Location: Toledo, Ohio
Primary reads 1450 ohms and the secondary reads 8000 ohms. I am using an ARBE-III eliminator which I use for all of my coffin style radios
The replacement transformer was checked 4 times for correct connections. I think if I connected the replacement incorrectly I would not hear any audio thru the headphones.

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Last edited by Jim Dutridge on Sep Thu 02, 2021 12:02 am, edited 1 time in total.

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 Post subject: Re: Help with Freshman Masterpiece
PostPosted: Sep Wed 01, 2021 11:54 pm 
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Joined: May Sat 30, 2015 11:49 pm
Posts: 2038
Location: Keystone Heights, FL, USA 32656
I think you meant “not hear…”?

Voltages check OK?

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 Post subject: Re: Help with Freshman Masterpiece
PostPosted: Sep Thu 02, 2021 6:29 am 
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Location: La Mesa Califonia
This should help.


Attachments:
freshmanmasterpiece.png
freshmanmasterpiece.png [ 403.2 KiB | Viewed 847 times ]
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 Post subject: Re: Help with Freshman Masterpiece
PostPosted: Sep Sun 05, 2021 3:36 pm 
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Posts: 7784
Location: Toledo, Ohio
thunderbird281 wrote:
This should help.


Thanks for that drawing. Its very close to what my radio shows except mine has terminal connections for the internal horn that are connected parallel to the speaker jack and the grid leak is paralleled with a 250pF capacitor.

Now as far as voltages go, the plates on the first 2 and last 2 tubes read 95 volts and their grids read 0. As for the middle 01A, the plate reads 50 volts and the grid reads 4.5 volts.

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 Post subject: Re: Help with Freshman Masterpiece
PostPosted: Sep Sun 05, 2021 6:13 pm 
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Joined: May Sat 30, 2015 11:49 pm
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Location: Keystone Heights, FL, USA 32656
Those voltages look OK, to me.

You should get a nice hum when touching the detector grid with a meter probe. This indicates that the audio section is working.

Measure resistance between the tuning condensers stator and rotor, while adjusting full open and full closed. Should be low resistance but not zero, and not change as the rotors are moved.

Measure resistance from ANT to GND connections.

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 Post subject: Re: Help with Freshman Masterpiece
PostPosted: Sep Sun 05, 2021 7:58 pm 
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Location: S. Dartmouth MA 02748-1225 USA
Jim,

The "A" voltage at the terminals on the radio should be 6 to 6.6 volts with the tubes burning.

FWIR Freshman used a lot of hollow rivets to electrically join various connections on the Bakelite chassis. These joints become problematic with 95 years passing. Suggest careful soldering all the strap connections to reduce any RF resistance that our meters cannot measure. Careful, Bakelite does blister if overheated... Clean off all the grey lead color from the tips of the tube pins.

Chas

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 Post subject: Re: Help with Freshman Masterpiece
PostPosted: Sep Tue 07, 2021 9:14 pm 
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Location: Toledo, Ohio
Chas wrote:
Jim,

The "A" voltage at the terminals on the radio should be 6 to 6.6 volts with the tubes burning.

FWIR Freshman used a lot of hollow rivets to electrically join various connections on the Bakelite chassis. These joints become problematic with 95 years passing. Suggest careful soldering all the strap connections to reduce any RF resistance that our meters cannot measure. Careful, Bakelite does blister if overheated... Clean off all the grey lead color from the tips of the tube pins.

Chas


Went thru and cleaned and resoldered all connections and cleaned up the tube pin ends. Now I have a bit more volume but alot of birdies and whistles. I can tune in a station but it comes with birdies/whistles. Even though I have already done it I am going to go back and reclean all of the tube socket connections.

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 Post subject: Re: Help with Freshman Masterpiece
PostPosted: Sep Wed 08, 2021 9:33 pm 
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Location: Toledo, Ohio
Cleaned up the tube socket connections and reflowed the connections on the tuning capacitors. I now have good volume and am able to tune between the 2 strongest stations here in town although the stronger of the 2 bleeds thru on the other. Also the sound is rather distorted.

Another thing I don't understand is why they paralleled the inner horn and external horn connections. it doesn't make any sense unless it was an extremely early try at remote speakers.

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 Post subject: Re: Help with Freshman Masterpiece
PostPosted: Sep Wed 08, 2021 10:16 pm 
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Jim Dutridge wrote:
Cleaned up the tube socket connections and reflowed the connections on the tuning capacitors. I now have good volume and am able to tune between the 2 strongest stations here in town although the stronger of the 2 bleeds thru on the other. Also the sound is rather distorted.

Another thing I don't understand is why they paralleled the inner horn and external horn connections. it doesn't make any sense unless it was an extremely early try at remote speakers.
Distorted sound can be caused by a number of things. The sound reproducer impedance may not be a good match.

Quote:
so I replaced it with a solid state replacement that someone here on ARF was selling
This artificial transformer may not match.

A, B, C voltages may be way out, the detector may require a different grid leak and a B voltage change.

One or more tubes may be gassy.

Overload of the RF stages can also be responsible too. Direct ground connection is helpful to deal with local strong stations but failing that radio fans would build adjustable traps to reduce the RF level of the offending station and install on the antenna lead-in...

----------------------------------------------------------

The horn jack may be an oversight, a dual switching jack would permit the internal horn to play and when an external horn is plugged into the jack the internal horn is automatically disconnected...

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 Post subject: Re: Help with Freshman Masterpiece
PostPosted: Sep Wed 08, 2021 10:34 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Bristol TN 37620
Just a suggestion - try lower B+ (like 67 instead of 90)
and 22 instead of 45. Also raise your A volts as Chas
suggests.


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 Post subject: Re: Help with Freshman Masterpiece
PostPosted: Sep Wed 08, 2021 11:31 pm 
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Location: Toledo, Ohio
I'll try the suggestions tomorrow, thanks.

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 Post subject: Re: Help with Freshman Masterpiece
PostPosted: Sep Thu 09, 2021 8:56 pm 
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Location: Toledo, Ohio
Lowering the voltages for the det and amp supplies really didn't change much as far as the distortion goes. Already had the filament supply up to 6 volts. Headphones sound pretty good and have plenty of volume.

Its hard to tell whether its a problem with the internal driver or not since the horn and internal speaker connections are parallel. I am going to try and replace the jack so that the internal speaker is disconnected when the horn is connected.

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 Post subject: Re: Help with Freshman Masterpiece
PostPosted: Sep Thu 09, 2021 10:57 pm 
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Location: Keystone Heights, FL, USA 32656
Why not disconnect the internal driver for a test? Instead of modifying the radio.

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 Post subject: Re: Help with Freshman Masterpiece
PostPosted: Sep Thu 09, 2021 11:19 pm 
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Freshman did make jacks, or at least jacks with their logo so a closed circuit may be around for an authentic restore.

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 Post subject: Re: Help with Freshman Masterpiece
PostPosted: Sep Thu 09, 2021 11:26 pm 
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That's what I was thinking. The way it's wired, plugging in an external horn speaker does not disconnect the internal speaker.

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 Post subject: Re: Help with Freshman Masterpiece
PostPosted: Sep Fri 10, 2021 12:26 am 
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It may be a jack mis-wire. If it is a single circuit jack there will be only one blade, if is a switcher, there will be two or more blades. Tricky, because the frame is not supposed to be live with B+, so there should be two sets of blades that connect the frame and disconnect the internal horn. Any other connection the jack will be hot with 90 volts. The frame has to be on an insulated panel or insulated washers. Polarity has to be correct for the remote horn so horn + goes to circuit + and horn negative goes to plate.

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 Post subject: Re: Help with Freshman Masterpiece
PostPosted: Sep Fri 10, 2021 4:34 am 
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Chas -I don't think it was a mis-wire, my 5J5 was the same way and the original schematic shows it wired that way. I have no idea why they would do that, so I had to modify the jacks and rewire it. You should remember that thread (link below). :wink: Re-wiring the jacks also eliminated another problem, an annoying howling sound the radio would make when it played.

Original schematic......

Attachment:
Freshman 5F5 - Early - Windows - No C Battery.jpg
Freshman 5F5 - Early - Windows - No C Battery.jpg [ 823.71 KiB | Viewed 584 times ]



Here's a blow-up of the section with the new wiring setup...

Attachment:
Freshman 5J5 Updated Wiring 05-04-2021.jpg
Freshman 5J5 Updated Wiring 05-04-2021.jpg [ 250.71 KiB | Viewed 588 times ]


Now it works like it should. Plug in headset or external speaker and the built in speaker cuts out.

Jim- This thread might help with the re-wiring and jack modifications..... viewtopic.php?f=6&t=394753&p=3360399#p3360399

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 Post subject: Re: Help with Freshman Masterpiece
PostPosted: Sep Fri 10, 2021 9:59 am 
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Location: Toledo, Ohio
Thanks Dan.

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