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 Post subject: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Sun 16, 2021 2:56 pm 
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Joined: May Sun 16, 2021 1:18 pm
Posts: 15
I'm new to this forum and could sure use some help diagnosing a problem with an RCA SHF-5 Orthophonic Console. The problem I'm having is no sound when the changer is plugged into the Phono input jack on the side of the AMP. This AMP has 4 jacks, PHONO, TUNER, TAPE, STEREO. When I plug the changer into the STEREO jack with the selector set to STEREO I get sound at about half volume with no vol adjustment or Bass/Treble adjustment.
My understanding is this is normal and was designed for a "stereo tape player" that could be added through these 2 inputs.
My skills are limited, I can replace components in these vintage units but I have difficulty reading schematics and troubleshooting issues like this one. I have replaced all electrolytic and film caps but have not changed any ceramic caps or resistors. I have swapped out the 6CG7 and 6V6 tubes and checked continuity on the selector switch to eliminate these as a potential problems. I have also tried plugging the changer into the TUNER jack with no sound as well.
I could use some recommendations on where to focus my efforts to correct this issue.

Attached is the schematic


Thanks in advance.
Guy K


Attachments:
20210330_075159.jpg
20210330_075159.jpg [ 2.77 MiB | Viewed 663 times ]
RCA SHF-5 Orthophonic.pdf [884.79 KiB]
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 Post subject: Re: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Sun 16, 2021 6:03 pm 
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Joined: Dec Mon 23, 2019 5:52 pm
Posts: 509
You're correct about plugging the cartridge into the "stereo" jack, it by-passes the first two stages of amplification. If the caps have been replaced, and V1, the first 6CG7 is lighted and tests good, most likely you have a bad plate resistor. Check/replace the 82K (R7 gray-red- orange) connected off of pin 1 of V1. Also, check/replace the 120K resistor (R17 brown-red-yellow) off of pin 6 of the same tube.


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SHF-5.jpg
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 Post subject: Re: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Sun 16, 2021 10:38 pm 
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Joined: May Sun 16, 2021 1:18 pm
Posts: 15
Thanks for the reply. I disconnected one side of each of the resistors and got readings of 90.4K on R7 and 125.5K on R17. Do you think these are too high and should be replaced?

Thanks


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 Post subject: Re: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Mon 17, 2021 3:13 am 
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Joined: Dec Mon 23, 2019 5:52 pm
Posts: 509
Those readings should be okay, they are within the 20% tolerance for those resistors.Did you take any voltage readings? R17 is fed from the 235 volt source, and R7 is the only thing being fed from the 215 volt source. R18 or R8 being bad would only affect this part of the amp. Did you try the amp and have this issue before recapping? Do you hear any noise in the speaker when the volume control is rotated? How about pulling V1 out with the amp on and listening for a "pop". Other than the plate resistors, which appear to check good, the only other parts that could completely kill a stage would be the cathode resistors R9 off of pin 3 of V1, and R20 off of pin 8.


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 Post subject: Re: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Mon 17, 2021 12:36 pm 
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Joined: May Sun 16, 2021 1:18 pm
Posts: 15
I'll try your suggestions later today and see what I find. When I first turned on the unit prior to recap, I got some strange noises, so I turned it off and proceeded with the recap prior to tuning it on again. I'm getting a reading of 175K on R22 which is supposed to read 82K. Could this be the culprit? I don't have any 82K resistors so I'll have to order to replace.
I appreciate the help!


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 Post subject: Re: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Mon 17, 2021 8:40 pm 
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Location: Mountains of Mourne. Ireland.
Here's a one-page schematic.


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SAMS 387-13.pdf [3.09 MiB]
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 Post subject: Re: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Wed 19, 2021 1:09 pm 
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Joined: May Sun 16, 2021 1:18 pm
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Thanks for the Schematic. I actually have it but my problem is the ability to read it and trouble shoot from the schematic.


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 Post subject: Re: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Wed 19, 2021 10:25 pm 
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Joined: May Sun 16, 2021 1:18 pm
Posts: 15
There is no noise from the speakers when the volume is turned all the way up and the selector is set to phono. There is a “pop” when I remove V1. I checked the voltages and there seems to be a significant issue there. Here is what I get:
5Y3 Rectifier
2 – 325 DC
4 – 315
6 – 315
8 – 325 DC

V1 V2
1 – no reading 1 – 135 V
3 – 220 V 3 – 5 V
6 – 104 V 6 – 148 V
7 – No reading 7 – 30 V
8 – 4 V 8 – 43 V

V3 V4
3 – no reading 3 – no reading
4 – 300 V 4 – 300 V
8 – 20 V 8 – 20 V

Especially troubling are the readings on V1 pins 1, and 3. V2 is off on most the voltages. No readings on pins 3 of V3 and V4. I tried 2 different 6CG7 tubes for V1 and got the same readings. This is a good lesson on getting voltages!


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 Post subject: Re: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Wed 19, 2021 10:30 pm 
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Joined: May Sun 16, 2021 1:18 pm
Posts: 15
The copy and paste didn't come out right. It lumped V1, V2 together and V3,V4 also. The pin numbers separate the readings


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 Post subject: Re: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Thu 20, 2021 12:36 am 
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Joined: May Sun 16, 2021 1:18 pm
Posts: 15
I found a major problem that can explain some of these voltage readings. Somewhere along the line I connected R7 to the terminal where R5 and R4 connect to pin 2 of V1. I could use some help determining what components may have been damaged by this blunder.
Here are the updated voltages:
V1 - Pins 1-235V, 3-16V, 6-114V, 8-4V
V2 - Pins 1-146V, 3-5V, 6-150V, 7-31V, 8-43V
V3 - Pins 3-320V, 4-306V, 8-20V
V4 - Pins 3-320V, 4-306V, 8-20V

Any thoughts on damaged components would be very helpful.
Thanks


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 Post subject: Re: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Thu 20, 2021 2:51 am 
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Joined: Dec Mon 23, 2019 5:52 pm
Posts: 509
I don't think anything was damaged by connecting R7 incorrectly. The only voltage issue I see is on V1. If you have 235 on pin 1, it means the tube is not drawing, but if it's not drawing there should be zero volts on pin 3. Reasons for pin 1 being so high could be, bad tube, tube socket connector not making contact with the tube pin, or a wiring error involving R6, R7, or C4. Remove V1 and see if you still get 16 volts on pin 3.


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 Post subject: Re: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Thu 20, 2021 12:54 pm 
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Joined: May Sun 16, 2021 1:18 pm
Posts: 15
I'll check your suggestions. Would the incorrect wiring damage a 6CG7 tube? I swapped out 2 tubes and got the same readings. I am reluctant to swap another if these voltages caused damage.
With the wiring error, I had 220V coming off #3 on V1. The electrolytic C2-C is a 25V cap. Do you think that cap is blown and if so would it be a factor with these voltages? I struggle with how caps and resistors work. I was also wondering why there isn't a voltage drop on pin 1 after R6?
Thanks for your help, this is a great educational experience.


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 Post subject: Re: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Thu 20, 2021 4:10 pm 
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Joined: Dec Mon 23, 2019 5:52 pm
Posts: 509
The wiring error you described should not have caused any damage. I don't know how there could have been that much voltage on pin 3 without resistor R9 burning up and cap C2C exploding. Can you post some pictures of that area of the chassis?


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 Post subject: Re: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Thu 20, 2021 4:38 pm 
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Joined: May Sun 16, 2021 1:18 pm
Posts: 15
When I can I'll take some pics and also take a look at your earlier suggestions. I may have been taking a reading off pin 2 (at 220V) and listed it as 3 especially since I don't think I would have checked 2 for voltage???


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 Post subject: Re: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Fri 21, 2021 11:26 am 
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Joined: May Sun 16, 2021 1:18 pm
Posts: 15
I reviewed photos of the chassis prior to the recap and compared the two and I am fairly confident it is wired correctly. When I remove V1, there is no voltage on pin 3. I may have found an issue with R34 (2200ohm 1 watt) which is reading 2900. Would this cause the high voltage readings that I am seeing at V1 and V2?
I also used 33 microfarad caps vs 35 for C1 A&B. Could this be an issue?


Attachments:
20210520_173159.jpg
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20210520_173211.jpg
20210520_173211.jpg [ 861.16 KiB | Viewed 465 times ]
20210520_173244.jpg
20210520_173244.jpg [ 923.96 KiB | Viewed 465 times ]
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 Post subject: Re: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Sat 22, 2021 3:06 am 
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Joined: Dec Mon 23, 2019 5:52 pm
Posts: 509
R34 is close enough that it should not cause a problem. Also, the cap values are okay. From your pictures everything does look correct. The only thing I see, and it may just be the angle of the picture, the socket connectors on V1 look like they may or may not be making contact with some of the tubes pins. I always remove the tubes and squeeze those "plates" together with long nose pliers and insert the tube straight in trying to avoid rocking it side to side so they don't spread apart again.


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 Post subject: Re: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Sat 22, 2021 12:04 pm 
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Joined: May Sun 16, 2021 1:18 pm
Posts: 15
I have pinched all the pins together and also checked the voltages at the tip of the tube pins, so I'm fairly confident that there is good contact at the socket. This issue has me so frustrated I'm very close to throwing in the towel and scraping the whole project. I hate to part this unit out but I'm running out of options. I'll try any additional recommendations to get this console operating.
Thanks for your help.


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 Post subject: Re: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Sat 22, 2021 3:02 pm 
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Joined: Jan Wed 16, 2013 12:04 am
Posts: 2411
Location: 77001
Sometimes we all need a mental break from a frustrating
project, before we give up on it.
Take several days off.

1. What input source are you using for the audio signal ?

2. Have the tubes been checked on a tester ?
Check that tube pins are not loose.

3. Does anyone recommend the OP to sequentially check
the control grids on the tubes with an insulated
wire probe ? (the poor man's signal tracer ?)

Or use a signal generator ?

Hotwax


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 Post subject: Re: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Sat 22, 2021 10:06 pm 
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Joined: Dec Mon 23, 2019 5:52 pm
Posts: 509
One more thing to try is to take resistance measurements on V1 and compare them to what the Sams resistance chart says. A stray piece of solder, a strand of wire lodged somewhere or a shielded cable that was over heated and melted can cause your issue. After correcting the initial wrong connection of R7 do you still not get any sound at all using the phono input? Does it still sort of work using the stereo input? How about plugging the changer into the tape jack and listen for any sound while rotating the input selector switch.When the selector switch is in the phono, tuner, or stereo setting the tape jack is an output jack for recording, but feeding a signal into the "out" jack does by-pass the first section of V1 and could tell us if the second section is working or not. You won't get a lot of sound because of R11 being such a low value, but something should come through.


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 Post subject: Re: RCA SHF-5 Phono/Tuner input problem
PostPosted: May Sun 23, 2021 3:33 pm 
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Joined: May Sun 16, 2021 1:18 pm
Posts: 15
First of all I want to thank rcadanny and Hotwax for the help and encouragement in pressing forward with this project. It turns out the problem was simple but took a while to diagnose. I was preparing a long drawn out post with voltage reading pictures etc...and while taking the resistance readings on V1 I discovered no continuity between V1 pin 3 and the connection point of R9/C2. It turned out to be a bad solder that occurred on the recap. This thing is working correctly and sounds phenomenal!
I'm going to be putting it back together and when I'm finished I hope to get your help on a Magnavox 294-C that has an issue. I'll put together a post soon.

Thanks for help!!!

Guy


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