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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Nov Wed 24, 2021 6:49 pm 
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Joined: May Sat 08, 2021 5:45 am
Posts: 19
jrehkopf wrote:
How many wires are connected to your speaker rectifier? I would guess 2 wires to the field and two wires from the transformer? It is a full wave rectifier, I think. Like this, except the field coil is instead of the battery shown.
Attachment:
Rectifier.jpg


Confirmed, thank you, it's definitely a full wave bridge - I traced the criss-cross wires and took measurements, and while the forward and reverse breakdown voltages are way too similar, there's still a small consistent difference that allowed me to determine the direction of the diodes. Sucker definitely needs to be replaced.

I've been feeding the speaker field with a 6.3V bench supply, and now it sounds pretty excellent! Definitely wanna replace that surround for better bass response. Music played into it definitely comes out with certain parts/frequencies weirdly accentuated or rolled off, but guitar sounds KILLER through it!! The detail and crispness in the midrange are pretty unreal, I don't think it'd be great for lead and super high notes, but as a rhythm player it suits me just fine!

However, I would like the ability to connect a more full-range, more modern PM speaker at my option, so now I am determining the necessary speaker impedance.

I would love to confirm with someone - do the output tubes see a reflected impedance of the output transformer (in speaker base) and output choke (in amplifier) in parallel? Would it be the impedance of the whole choke, or just one winding? My best guess is that the two paths to ground are through one half of the winding, and through OPT plus one half of the winding.

This community is really generous, thank you immensely for all your help so far!


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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Nov Wed 24, 2021 6:51 pm 
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Would also be very grateful for info on replacing the surround in this sort of speaker!


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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Nov Wed 24, 2021 9:18 pm 
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Location: Dayton Ohio
You can see how I do it with a piece of chamois cloth (which is goat hide) that I bought in the automotive department of Walmart.

https://antiqueradios.com/forums/viewto ... 8&start=20

Speaker manufacturers of the time used some sort of animal hide for the surround.
Stromberg Carlson advertised they used Carpincho leather which is the hide of a Capybara, a large rodent of South America.

-Steve

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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Nov Wed 24, 2021 11:41 pm 
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azenithnut wrote:
You can see how I do it with a piece of chamois cloth (which is goat hide) that I bought in the automotive department of Walmart.

https://antiqueradios.com/forums/viewto ... 8&start=20

Speaker manufacturers of the time used some sort of animal hide for the surround.
Stromberg Carlson advertised they used Carpincho leather which is the hide of a Capybara, a large rodent of South America.

-Steve


I had just found some of your excellent advice on other threads, but this is even more suited to what i'm doing, thank you! I'm thinking I will use bedsheet fabric for the surround (i'm vegan, so i'd prefer not to use chamois), and use an embroidery hoop for exactness, but I still need to do more research, and examining of the unit.


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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Nov Thu 25, 2021 1:52 am 
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Location: Mission Viejo, southern California
I've done several using the chamois I got from Autozone, and GC Service Cement https://www.tubesandmore.com/products/c ... ice-cement


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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Nov Thu 25, 2021 2:40 am 
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The first few I did was with cloth such as a bedsheet. Some cotton muslin cloth would work well. I only went to chamois because its close to what was originally used.

The glue I used is now discontinued, but I've managed to get by with other adhesives. I like rubber cement best as it holds and is flexible.
GC Service Cement is good, but is very rigid. Care must be taken not to get it where the cloth needs to flex.

The embroidery hoop is a lifesaver! :D

-Steve

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-Pre-War FM
Consoles and floor models, the bigger, the better!


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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Nov Thu 25, 2021 3:04 am 
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By the way, I just noticed that I have a PDF of the service manual for the Mohawk 226-227, Lyric 60, 61, 62, 65, 66, 70, 73, 75, 80, 83, 84, 85, 86, 88, 90, 96, and Model D.

Here is my Mohawk rectangular box radio (power switch loose, rubber wiring throughout needs to be changed) and speaker.


Attachments:
Mohawk Radio and Speaker.jpg
Mohawk Radio and Speaker.jpg [ 484.38 KiB | Viewed 297 times ]
Mohawk Radio lid open.jpg
Mohawk Radio lid open.jpg [ 584.86 KiB | Viewed 297 times ]
Mohawk Pyramonic Speaker tag.jpg
Mohawk Pyramonic Speaker tag.jpg [ 590.1 KiB | Viewed 297 times ]
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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Nov Thu 25, 2021 5:27 am 
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Joined: Apr Sun 08, 2007 6:47 am
Posts: 5208
Location: British Columbia
mxrshiver wrote:
Arran wrote:

You can use film caps, or find motor run caps of the same values, Mouser sells some made by Panasonic that will work, internally fused apparently, I think Vishay makes similar ones. Many just don't bother and go with the regular yellow ones you see everywhere, but Mouser's prices are usually pretty good, and since most would hind the new ones inside the old can it doesn't matter what they look like.
Regards
Arran


I severed the wires to the tower and was able to neatly fit replacement caps on the bottom side. I doubled the values (still only 4uF for the first filter, well below what I believe the 171A's limit of 20uF is) just to get some tighter bass - i am eventually going to be optimizing the aux input for guitar. I used electrolytics for everything except the 0.1uF caps in parallel with the chokes, for which i used polypropylene - was it a bad idea to use electrolytics there?

I'm getting better HT+ now - the 171A's were already okay, but the rest were quite low, now they're all at least within 20% of nominal. Still going to have to change one or two of the power supply dropping resistors.

I've been taking readings on the 171A's to try and determine the idle current, but I think I'm doing something wrong...

they have 183V on the plate, and a bias voltage of -27.4 read between the grid and either leg of the heaters. this worried me because judging by the datasheet graph, that should put me at 80mA or so, way above their capabilities!

however, measuring a voltage drop of 27.4 between either leg of the heater and ground, across the cathode resistor (measured at 1.1Kohms), this tells me I should be pulling 25mA, 12.5mA per tube... which should correspond with a bias voltage of 52 or so, way off mark.

does each tube somehow see double the bias voltage i'm measuring? they both tested NOS and well matched, so that's not the issue.


It's not a good idea to use small value electrolytics in these as they are not really suited to handle the ripple current. They have a habit of heating internally, and shorting out, someone I know of tried these in a Philco 20 and they exploded in about a year.


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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Nov Thu 25, 2021 5:29 am 
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Joined: Apr Sun 08, 2007 6:47 am
Posts: 5208
Location: British Columbia
mxrshiver wrote:
jrehkopf wrote:
How many wires are connected to your speaker rectifier? I would guess 2 wires to the field and two wires from the transformer? It is a full wave rectifier, I think. Like this, except the field coil is instead of the battery shown.
Attachment:
Rectifier.jpg


Confirmed, thank you, it's definitely a full wave bridge - I traced the criss-cross wires and took measurements, and while the forward and reverse breakdown voltages are way too similar, there's still a small consistent difference that allowed me to determine the direction of the diodes. Sucker definitely needs to be replaced.

I've been feeding the speaker field with a 6.3V bench supply, and now it sounds pretty excellent! Definitely wanna replace that surround for better bass response. Music played into it definitely comes out with certain parts/frequencies weirdly accentuated or rolled off, but guitar sounds KILLER through it!! The detail and crispness in the midrange are pretty unreal, I don't think it'd be great for lead and super high notes, but as a rhythm player it suits me just fine!

However, I would like the ability to connect a more full-range, more modern PM speaker at my option, so now I am determining the necessary speaker impedance.



Try tightening the bolt going through the center, it's a copper oxide rectifier so they don't really go bad like a selenium one can


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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Nov Thu 25, 2021 5:12 pm 
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Joined: May Sat 30, 2015 11:49 pm
Posts: 2048
Location: Keystone Heights, FL, USA 32656
mxrshiver wrote:
Would also be very grateful for info on replacing the surround in this sort of speaker!

I used a pre-made foam surround kit from these guys https://www.speakerworks.com/foam-surro ... g-s/63.htm.

This assumes that the cone is still in good condition. Carefully remove the old surround remains.Then follow instructions and glue in the new surround.
Attachment:
DSC02540.JPG
DSC02540.JPG [ 190.66 KiB | Viewed 281 times ]

Attachment:
DSC02553.JPG
DSC02553.JPG [ 250.23 KiB | Viewed 281 times ]

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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Nov Thu 25, 2021 5:22 pm 
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Location: Mission Viejo, southern California
Thank you, that looks much easier and faster than making a surround from chamois.


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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Nov Thu 25, 2021 5:37 pm 
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Location: Dayton Ohio
Yep, that is another way to do it.

It looses originality, but will work great!

-Steve

_________________
Radio Interests
-Zenith
-Sparton
-Pre-War FM
Consoles and floor models, the bigger, the better!


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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Nov Fri 26, 2021 9:10 am 
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Joined: Apr Sun 08, 2007 6:47 am
Posts: 5208
Location: British Columbia
azenithnut wrote:
Yep, that is another way to do it.

It looses originality, but will work great!

-Steve


Until the foam disintegrates that is, there is also the problem of it sticking out too far and hitting the back of the board in from of it. Why not just do it right the first time with chamois leather?


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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Nov Tue 30, 2021 8:21 am 
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Arran wrote:
mxrshiver wrote:
jrehkopf wrote:
How many wires are connected to your speaker rectifier? I would guess 2 wires to the field and two wires from the transformer? It is a full wave rectifier, I think. Like this, except the field coil is instead of the battery shown.
Attachment:
Rectifier.jpg


Confirmed, thank you, it's definitely a full wave bridge - I traced the criss-cross wires and took measurements, and while the forward and reverse breakdown voltages are way too similar, there's still a small consistent difference that allowed me to determine the direction of the diodes. Sucker definitely needs to be replaced.

I've been feeding the speaker field with a 6.3V bench supply, and now it sounds pretty excellent! Definitely wanna replace that surround for better bass response. Music played into it definitely comes out with certain parts/frequencies weirdly accentuated or rolled off, but guitar sounds KILLER through it!! The detail and crispness in the midrange are pretty unreal, I don't think it'd be great for lead and super high notes, but as a rhythm player it suits me just fine!

However, I would like the ability to connect a more full-range, more modern PM speaker at my option, so now I am determining the necessary speaker impedance.



Try tightening the bolt going through the center, it's a copper oxide rectifier so they don't really go bad like a selenium one can


tried it, tightened almost until i couldn't anymore. breakdown voltage rose maybe 0.01V... really think i might have ruined the oxidized layer with de-oxit!


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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Nov Tue 30, 2021 8:29 am 
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Posts: 19
Arran wrote:
azenithnut wrote:
Yep, that is another way to do it.

It looses originality, but will work great!

-Steve


Until the foam disintegrates that is, there is also the problem of it sticking out too far and hitting the back of the board in from of it. Why not just do it right the first time with chamois leather?


i've got about 5/16" of felt between the metal rim and the wood of the cabinet, and the excursion of this speaker is very small, so i'm not too worried about the lip of the foam, especially with a 6" cone. my hands are a bit shaky and this is definitely not my area of expertise, so i might just get a simple kit for installing a foam surround from someone reputable, if it's a viable option. longevity is a big concern - if anyone can compare bedsheet, foam and chamois/leather on that scale i'd be grateful. leather seems to have held up unilaterally poorly, but at 90+ years that's hardly a comparable observation haha


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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Nov Tue 30, 2021 8:34 am 
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Arran wrote:

It's not a good idea to use small value electrolytics in these as they are not really suited to handle the ripple current. They have a habit of heating internally, and shorting out, someone I know of tried these in a Philco 20 and they exploded in about a year.


thanks for the heads up! these are all tested to 500V on a Heathkit C1 so i figured i'd have enough overhead on voltage spikes, but if they're breaking down due to heat that's another thing.

well... the 80 is supposedly good up to 20uF. any issue with me slapping on say, 15's or 16's across the board?


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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Nov Tue 30, 2021 8:38 am 
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Joined: May Sat 08, 2021 5:45 am
Posts: 19
FStephenMasek wrote:
By the way, I just noticed that I have a PDF of the service manual for the Mohawk 226-227, Lyric 60, 61, 62, 65, 66, 70, 73, 75, 80, 83, 84, 85, 86, 88, 90, 96, and Model D.

Here is my Mohawk rectangular box radio (power switch loose, rubber wiring throughout needs to be changed) and speaker.


*blinks*
that's the same model, for certain! what a beaut! and you have the service manual for practically the entire Lyric line for the duration of All American Mohawk's existence... that is beyond brilliant! would you be willing to share? the plate on that speaker is gorgeous as well.


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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Nov Tue 30, 2021 8:43 am 
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many thanks to FStephenMasek, jrehkopf, and especially azenithnut for all of the excellent advice on replacing the surround. it makes me sleep better at night knowing you wizards are willingly pouring your knowledge onto the permanent record of an internet public forum... anyway, thanks to you i have several excellent options to proceed!


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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Nov Tue 30, 2021 5:03 pm 
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Location: Mission Viejo, southern California
Glad to help!

mxrshiver wrote:
Arran wrote:
any issue with me slapping on say, 15's or 16's across the board?
Yes, too large a first capacitor and the B+ will be much too high. I encountered that with my GM Dayfan A5003, until I used a much smaller value film capacitor for the first one.


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 Post subject: Re: All American Mohawk Corp Lyric Model 83
PostPosted: Dec Wed 01, 2021 1:56 am 
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FStephenMasek wrote:
Glad to help!

mxrshiver wrote:
Arran wrote:
any issue with me slapping on say, 15's or 16's across the board?
Yes, too large a first capacitor and the B+ will be much too high. I encountered that with my GM Dayfan A5003, until I used a much smaller value film capacitor for the first one.


polypropylene it is, then! perhaps that was the reason for the (seemingly random) supply voltage fluctuations i was getting from it the other day...

this is probably a real dumb question, but... what is the deal with the potentiometer in this model? it's the one just before the detector/phono input. assumed it's a volume, but whatever it is, it doesn't seem to work well, as there is no apparent connection to ground?! there's only one wire running to a single leg on it, there are no other legs for the wiper or ground... the knob has a notch that it clicks into that i believe effectively takes it out of the circuit.

in function with the AM signal, it seems to work intermittently, if that, and is never a smooth control, even though the multimeter reads a smooth gradient throughout its range, it's very clean, and the wiper seems to make contact the whole time... when playing guitar into the phono input, there's sometimes a small noise signal (hum) that increases slowly, that can usually be eliminated by turning the knob a full rotation until it clicks again...

any issue with me replacing this with a normal 75K log pot, and connecting it as shown on schematic? or a 100K, for that matter?


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