Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Dec Sun 17, 2017 1:29 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 36 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Fri 08, 2017 1:39 am 
Member
User avatar

Joined: Aug Tue 30, 2011 11:25 pm
Posts: 1100
Location: Charlevoix, Michigan, USA
My A-K 55C is working, but i have noticed that the sound is a bit "muddy" rather than sharp and clear. This is especially noticeable when I am playing music through an AM transmitter in the house, which sounds fine over other radios. The only things I have replaced, as far as components go, are the power supply capacitors and the line voltage caps. The "quality capacitor" was left in place. The tubes that have shields, have the shields in place, but the sheet metal cover that fastens in place with thumb nuts is missing. What could cause that "muddy" sounding audio? Where should I look first? And if it is the "quality capacitor", is there any way to disconnect it without digging into a tar block?


Top
 Profile  
 
 Post subject: Re: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Fri 08, 2017 2:01 am 
Member
User avatar

Joined: Aug Tue 30, 2011 11:25 pm
Posts: 1100
Location: Charlevoix, Michigan, USA
...Or, maybe I have the drive turned up too far on my transmitter?


Top
 Profile  
 
 Post subject: Re: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Fri 08, 2017 2:29 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 31407
Location: Maryland 20709, USA
As with all vintage sets, you must replace ALL waxed paper capacitors.

These are located in two rectangular metal cans screwed to the chassis walls.

The late version has a third metal can containing two line bypass caps.

- Leigh

_________________
73 de Leigh W3NLB
http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


Top
 Profile  
 
 Post subject: Re: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Fri 08, 2017 11:46 am 
Member

Joined: Sep Mon 05, 2011 1:42 pm
Posts: 805
Location: Philadelphia, PA
I was never pleased with the audio quality from my 55C.
Even listening to news or baseball games on the AK, listening fatigue occurs pretty quickly.
I have the same issue with my circa 1935 GE/RCA console.

Regards - Dan

_________________
Dan
N3DTF


Top
 Profile  
 
 Post subject: Re: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Fri 08, 2017 1:39 pm 
Member
User avatar

Joined: Jul Tue 15, 2008 6:13 pm
Posts: 4429
Location: Gretna, NE
Agree with Leigh.
Have you replaced all bypass, coupling, and filter caps yet?
Its no small job due to the caps all being sealed in metal cans, but once completed it makes a world of difference in sonic quality.
Here is a picture of capacitor cans being restuffed.
Attachment:
20170207_082307.jpg
20170207_082307.jpg [ 80.75 KiB | Viewed 253 times ]

_________________
http://www.vintagerestorationservices.com
Paul
...... how hard can it be?


Top
 Profile  
 
 Post subject: Re: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Fri 08, 2017 2:04 pm 
Moderator
User avatar

Joined: Feb Sun 01, 2009 2:56 pm
Posts: 9104
Location: Victoria, Australia
Not overlooking that that can is not completed I would, if no lining the can preferred to see shrink tube, or a sleeve on the wires on the top cap to ensure no shorting to the side.

As the originals may have been "outside foil"; I tend with modern caps like that in close proximity to shield them to prevent induction. I do it, as I have seen induction happen.

Marc


Top
 Profile  
 
 Post subject: Re: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Fri 08, 2017 2:59 pm 
Member
User avatar

Joined: Aug Tue 30, 2011 11:25 pm
Posts: 1100
Location: Charlevoix, Michigan, USA
My A-K 55C is a late model. I replaced all the filter caps in the big square can on top of the chassis ( they were small enough to mount UNDER the chassis on a terminal strip, in fact). It originally had three of the "sardine cans" under the chassis, but at some time in the radio's working life, someone replaced the line cord bypass caps with a couple of paper and foil ones (looked like 1930's or 1940's vintage ones) and eliminated that "can" altogether. I replaced those caps with a couple of X/Y rated ones, which are safer for line bypass use (if they fail, they "open" short).

I have not, however, touched the other two "sardine cans" under the chassis (they would be the middle and right hand ones, if you are looking at the underside of the chassis with the cans at the upper edge). The line bypass caps would have been in the (now missing) left hand can.


Top
 Profile  
 
 Post subject: Re: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Fri 08, 2017 3:35 pm 
Moderator
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 10256
Location: Latham NY
Seems to me just about all the old TRF sets I have worked on don't have the real clear sound we get from a more modern superhet radio that has AVC and diode detection.


Top
 Profile  
 
 Post subject: Re: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Fri 08, 2017 3:49 pm 
Member

Joined: Jan Mon 16, 2012 4:15 pm
Posts: 3612
Location: Near Brandon, Iowa
Have you done the obvious stuff like measuring the B+ voltage, grid bias voltages for the audio driver and output tubes, and testing the detector and three audio stage tubes for emission? Low B+ voltage, incorrect grid bias voltage (which can be a byproduct of low B+ voltage) and low tube emission can trash the sound quality, either singularly or in concert with each other. An incorrectly-rebuilt, contaminated, or damaged, speaker can also be the source of poor sound quality. The simplest way to check this is to disconnect the voice coil (only) of the A-K speaker and patch in a PM speaker of known functionality.


Top
 Profile  
 
 Post subject: Re: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Fri 08, 2017 4:04 pm 
Member
User avatar

Joined: Aug Tue 30, 2011 11:25 pm
Posts: 1100
Location: Charlevoix, Michigan, USA
Voltages are within reasonable specs - checked that when I first replaced the PS filter caps. The radio had a 1930's vintage speaker installed when I first got it, and I replaced it with an F4. The F4 sounds better than the other one, probably because the field coil has a different resistance.


Top
 Profile  
 
 Post subject: Re: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Fri 08, 2017 8:49 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 31407
Location: Maryland 20709, USA
Rich K. wrote:
I have not, however, touched the other two "sardine cans" under the chassis

Those are waxed paper caps, and MUST be replaced like any others of that vintage.

Paul showed a nice photo of the proper method.

You can solder the base plate back in the can after replacing the caps, but that's not mandatory. If you do, it only needs solder in a couple of spots, not all the way around.

- Leigh

_________________
73 de Leigh W3NLB
http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


Top
 Profile  
 
 Post subject: Re: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Fri 08, 2017 8:51 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 31407
Location: Maryland 20709, USA
Lou deGonzague wrote:
Seems to me just about all the old TRF sets I have worked on don't have the real clear sound we get from a more modern superhet radio that has AVC and diode detection.
Hi Lou,

The AK 55 has a proper detector circuit, but of course no AVC.

It certainly is not a hi-fi receiver.

- Leigh

_________________
73 de Leigh W3NLB
http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


Top
 Profile  
 
 Post subject: Re: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Fri 08, 2017 9:00 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11541
Location: S. Dartmouth MA 02748-1225 USA
My experience with the 55 is to replace the caps in the "sardine" cans. Be mindful of the contents of the can that couples the plate circuits of the detector. Wrong component values here can result in poor audio characteristics. I have found discrepancies there and opted to duplicate the contents. The cans are numbered and there is data for the contents. The AC bypass can should be replaced if there are holes in the chassis provided. Please use a can numbered for the bypass and engrave numbers if a sub. can is used. By replacing the can there is less a chance for induced AC hum, dress any AC leads close to chassis, if there are a pairs of AC leads, twist them together 1 turn/inch.

There are many wire wound resistors in the chassis, they terminate to a hollow rivet and often have a poor connection. Remove screw from resistor and crush the rivet with pliers to remake the connection.

There is a pair of bias resistors in the B- return that shunt the speaker field. These often change value and may be unstable under current flow. Be sure to use at least 1 watt resistors, standard 10% vales will be close enough. Check the bias on the 45's, too negative will reduce output, too little bias will consume a lot of plate current and there will be distortion and HOT 45's. By altering the values of the bias resistors a good compromise can be found. The 45's will run warm but not hot to touch. Be concerned that the total value of the two bias resistor remains the same as published.

Some chassis returns are via a rivet to the chassis, after 80 years these often corrode even though it is not visible and does not indicate a poor connection with a typical ohmmeter. Solder all such chassis grounds to be sure, use a high wattage iron and an aggressive flux. If in doubt of skills, drill out hollow rivet and replace with machine screw and toothed lock washers...

The is a gimmick capacitor for the local distance circuit. this capacitor is made from two specific lengths of enameled magnet wire, twisted together a specific amount then covered with varnished cambric with a solder lug. It looks like a shabby piece of hookup wire... If it has been replaced with a wire, make a replica or plan to install a replacement series cap, FWIR the value is around 10 to 20 pf.

IMHO a TRF receiver is capable of good fidelity if working properly and does not have the narrow bandpass of a superhetrodyne. Like any other receiver, components and connections must be in good condition.

YMMV

Chas


Top
 Profile  
 
 Post subject: Re: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Fri 08, 2017 10:14 pm 
Member
User avatar

Joined: Aug Tue 30, 2011 11:25 pm
Posts: 1100
Location: Charlevoix, Michigan, USA
I found at least PART of the problem. Remember in my first post I said it was especially noticable when I used an AM transmitter? The transmitter is a 12AT6/12CS6 one I built from a kit offered in this forum a few years ago. I had the gain control turned way up to try to drown out the RF noise in the house from appliances, CFLs, and the WiFi. Modern radios don't seem to notice it as much, but in the AK, and even in my Radiola 60, as it turns out, it is WAY overmodulated. Turned the "volume" on the transmitter down - lots more static now, but not so muddy sounding. I will still replace the caps in the cans, though, eventually.


Top
 Profile  
 
 Post subject: Re: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Fri 08, 2017 11:35 pm 
Moderator
User avatar

Joined: Feb Sun 01, 2009 2:56 pm
Posts: 9104
Location: Victoria, Australia
Overhauling the set really is a must, the best you can get out of it will be when it is in spec & leaking caps do nothing to help, especially coupling ones. Being a radio one can always put an antenna on it & see what a Radio station sounds like. Where a DX switch was missing on an hacked STC here, I found 68pF switched into series with the antenna ideal. Distortion being gauged with an Oscilloscope.

Whist it is not likely to be causing the Muddy sound, which a speaker can be involved in, just like a Superhet they do need calibration when there are a series of tuned circuits, to ensure that they are all on the same frequency.

RFI is out of control & I am firmly of the opinion that the regulators both here and there, have reached the point of being ineffective. I would add that I have had two LED flood lights that I took back to point of sale for drowning out everything Radio on AM & FM.

Where there is a transformer in the set some improvements might be had by grounding the set & organizing line caps to go to it? RFI from power lines here is bad & lightning just as interesting. It is at the point where several power boards have been "got at" to deal with it. I also have plug in devices to remove line RF & deal with surges: That I have mentioned before.

If you build such devices, I suggest a well grounded metal, or fire rated box, as MOV's are known to explode.

Marc


Top
 Profile  
 
 Post subject: Re: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Fri 08, 2017 11:44 pm 
Member
User avatar

Joined: Aug Tue 30, 2011 11:25 pm
Posts: 1100
Location: Charlevoix, Michigan, USA
Thanks for all the advice. I will have to see what I have for caps in my parts box.

One other question: I do not have a ground hooked to my radio, and it receives without it. First, will it perform better with a ground wire? And second, since all the wiring in our house goes to plastic outlet boxes, the old "center screw ground connection" is not an option. What can I do for a ground, instead?


Top
 Profile  
 
 Post subject: Re: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Sat 09, 2017 12:15 am 
Moderator
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 10256
Location: Latham NY
It doesn't matter that the boxes are plastic. In a 3 wire system the ground wire is attached to the socket which carries that ground to the screw terminal on the plate.


Top
 Profile  
 
 Post subject: Re: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Sat 09, 2017 12:40 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1665
Location: Illinois
Try this: detune the set slightly one way or the other. This might pick up the sidebands better.

_________________
Doug


Top
 Profile  
 
 Post subject: Re: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Sat 09, 2017 12:59 am 
Member

Joined: Apr Thu 26, 2012 2:18 am
Posts: 257
Location: Tulsa, ok 74104
I thought I would reply to this and let you know that Paul dose some really good work. I had him recap my big can on my 55 and my radiola 60. due to a hand injury I received and was very pleased with the result and quality of his work
Benny


Top
 Profile  
 
 Post subject: Re: Atwater Kent Model 55C - "muddy" sound
PostPosted: Dec Sat 09, 2017 1:21 am 
Member

Joined: Apr Thu 26, 2012 2:18 am
Posts: 257
Location: Tulsa, ok 74104
so if I understand this the quality control cap is built into the speaker


Top
 Profile  
 
Post New Topic Post Reply  [ 36 posts ]  Moderators: Marcc, Norm Leal Go to page 1, 2  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: busterdog57, craterranch, simplex1040 and 19 guests



Search for:
Jump to:  


















Privacy Policy :: Powered by phpBB