Restoration of a Magnavox Concert Grand model 1ST800F

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Do you want to share my restoration of a Concert Grand?

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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by Bill Cahill on Wed May 13, 2015 4:37 pm

I'm not criticizing him. Just trying to save him money.

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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by jerryhawthorne on Wed May 13, 2015 4:54 pm

We know Bill.  If WC wants to spend some money, how about getting 6 of the 6V6 tubes matched?  I won't even go there.  Your eyesight Bill is about the equivalent of my hearing, eyesight is not great but hearing really sucks!  I don't know how you do what you do.  I need a lot of light and readers but not bad.  Hearing so bad I don't want to pick up a phone call.  Good luck WC, this radio should sound great when completed and sorry I wouldn't be able to hear it's great highs.  An audiophool I will never be, just give me bass.  
Onward and upward on the restoration WC.
Best to all,  Jerry

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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by Bill Cahill on Wed May 13, 2015 5:05 pm

Since the fourties Magnavox was vying for first place in true high fidelity. Too bad starting in the mid sixties they started going downhill. Until then they made some great stuff. Their worst were the SS stereos. I once had a friend in Detroit who had a 1972 console SS Magnavox in a sawdust, and, plastic console cabinet. It kept breaking down for several years. Then, the power transformer went POOF, and, he gave up on repairing it.
Transistors were always shorting out. Their tube stuff was far better.

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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by Wildcat445 on Wed May 13, 2015 5:05 pm

The point here is that the carbon resistors currently in these amplifiers are frequently found to have drifted double their rated value. Granted, it has been nearly 60 years, but drifted is drifted and drifted components are the main cause of troubles in Magnavox amplifiers. Why put known problematic components back in when more stable ones have been introduced and are in common usage since this instrument was built? I'm considering replacing the 1/2 watt resistors with 1 watt. I have been advised to be mindful of voltage ratings. I need a minimum of 350 volt components with surge voltages the higher the better. This is for resistors in the signal path. Power resistors will still be composition. I've put considerable time and research into this project and would like to err on the side of caution. I am not making recommendations nor am I criticizing any component or procedure. I am sharing what I am thinking and doing. I appreciate your all following along and thank you for your comments.

WC

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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by Wildcat445 on Wed May 13, 2015 5:12 pm

Jerry, I typically replace all the tubes in the amplifier. I did in the 9302 chassis in my Symphony and the 8102 chassis in the Imperial. The Concert Grand may be a different kettle of fish. First, it appears to be a low-hour instrument with none of the shorted, gassy or otherwise bad output tubes I typically find. Next, matched quads of Electro-Harmonix clear top tubes are $64. I will need four quads. And 4 rectifiers, and 4 12AX7's. That is nearly $400 in itself. I have had a member offer to send me some 6V6's, so in consideration of his generous offer, I may just use a mix of the original tubes and other NOS tubes and not go the new route. This may change, but right now that is the way I'm headed.

WC

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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by jerryhawthorne on Wed May 13, 2015 5:51 pm

With you all the way WC!
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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by Ragwire on Thu May 14, 2015 9:42 am

Don't forget to get "sonically transparent" resistors to go with your crunchy fizz tubes, or whatever...LOL
I could entertain myself all day reading audiophool advertisements.
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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by Wildcat445 on Thu May 14, 2015 10:30 am

12AX7's are the tubes that are supposed to have "crunchy fizz." Read the tube descriptions on AES's website. They surely don't write that bilgewater themselves. You're right, though. It makes me grin when I read stuff like that. Very Happy

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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by Wildcat445 on Thu May 28, 2015 3:07 pm

There have been some "political" considerations lately concerning the restoration of my Concert Grand. We had friends over for Memorial Day, so I had to re-position the Concert Grand with its front to the room. I can't work on it like that. Our friends wanted a demonstration of "that old thing", so I gave them a mini-concert. I warned them in advance that my CG was not hitting on all eight, so take that into consideration. The needle in this thing is beyond worn out. It is dangerously incompetent to even turn the turntable on with it in the cartridge. They wanted to hear "vinyl" of course. So I dug out an old record that I use for testing known defective record players. I don't care if I wreck the record. It was a "B" label tribute to Eddy Duchin. Full of skips and lots of noise. Our friends thought it was the most beautiful record they had ever heard. These people are in their late 60's or so, so they are not kids. And I must admit that I may begin to see the fascination with a Concert Grand. Even in its known state of desperately needing repair, that old worn out record being played by a worn out needle sounded pretty good. I put three additional notes on the schematic for use during repair/restoration. The 6E5 eye tube is essentially dead, the turntable speed is infinitely variable, depending on the mood of the drive tire, and the tone sounds more strangled the longer the instrument is on. As a side note, this instrument that draws 650 watts from the power line has the exact same size power cord on it as does a Magnavox AM-FM clock radio that pulls 60 watts. The power cord actually gets warm in use. Wonder if it would be considered sacrilege if I replaced it with a stouter cord? It seems silly to melt that cord and burn the house down all for the sake of originality. Another note I made was to not judge tonal output of this instrument when tuned to our local flea-power FM station. That station purposely dials back the bass so the old people can understand the noon news. This instrument also has a power supply hum, with hiss in the horns. That was the malady suffered by my Imperial, though it was much worse. I am typically of the opinion that the power supply filters used in Magnavox instruments are as good as there was and replacing them gains little. I may be modifying that opinion somewhat. The filter caps are of high quality, but these are also pushing 60 years old. These will all be replaced. I'm typically not a "can re-stuffer" so I need to develop an acceptable alternative plan.

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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by jerryhawthorne on Thu May 28, 2015 5:26 pm

Aw, come on WC restuff those e-caps! It is actually easy unless those are the "modern" ones with the twist tabs that mount them and typically at least one is soldered to the chassis. I need a much larger soldering iron to get those dang things out. I do hate those but once out restuffing is easy and fun. OK, I have a weird sense of humor?
Good luck and keep us informed on how your progressing. Never tried a beast like that but 3 Scott 800Bs and a Scott Metro.
Best, Jerry

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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by 75X11 on Thu May 28, 2015 5:43 pm

You might look into a clear plastic zip power cord of a heavier gauge. It wouldn't draw quite the attention of a solid color one.
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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by 75X11 on Thu May 28, 2015 7:23 pm

And maybe an interlock plug if that vacuum still has a taste for those cords. Very Happy
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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by Wildcat445 on Thu May 28, 2015 11:40 pm

I have come up with a plan to avoid the vacuum. I use bread ties and keep the cord tied up so it is just long enough to reach. I have a fairly new extension cord that could serve as a new power cord. The original one just looks too small to me. I have considered an interlock. Not only do I find them neat in appearance, they prevent the cord from being tangled if you want to move the instrument. I will have to drill the hole for the power cord out to the next size and get a larger strain relief for the cord. I want to fuse the individual components, but not the main power. That seems redundant, but am open to suggestions.

As for can stuffing. I am going to sort of restuff the cans. The problem is that I am going to series connect two 100uf @450 volt electrolytics to make a 50uf @900 volt filter cap for the amplifiers. These will be before and after the choke, with two 68uf @450 volt in series to replace the 30uf that powers the screens. That one goes in the restuffed can. The two before and after the choke go on a terminal strip. The cathode bypass cap will be mounted nearer the cathode resistor. The main power cap on the radio power chassis is a 30uf. I will restuff that can. There is a dual 30uf on the radio chassis to power the pre-amp section. I will restuff one of these, mount the other on a terminal. I do not remove the cans. I saw them in half, remove the guts, put in the new components, then use that high dollar shiny metal HVAC tape to put the can back together. You can't tell that it has been done like that.

It is the opinion of some that it is not advisable to connect electrolytic caps in series. The reason behind this thought is that the resistance is different on the series caps and that one cap may see more voltage than the other. To eliminate this concern, I connect a 300K (nominal) ohm resistor across the series caps. I did that on my Imperial, and the power supply is dead silent. This enhanced power supply will provide a little more oomph for driving the bass and will provide a margin of safety. The cathodes on the 5U4 rectifiers run at 320 volts at 117 volts line voltage. Higher line voltage will raise that some. 450 volt filter caps do not leave much room for error.

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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by 75X11 on Fri May 29, 2015 12:21 am

The separate fusing sounds good. That will localize any problems down the road.
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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by Wildcat445 on Tue Jun 02, 2015 5:19 pm

Let me refer you to this page for reference.

http://www.blackswampaudio.com/Tubes/USA_Manu_Codes.php

I have been digging around in my Concert Grand this morning, and thought I'd share what I found.

The tube sockets for the four rectifiers in the amplifiers have been changed as some point.  They are now bolted in rather than riveted.  The two rectifiers in the Channel 1 amp are RCA, the ones in Channel 2 are original (?) Magnavox branded.  I don't see codes on the RCA's but the Magnavox are coded 210-5943.  The four 12AX7 amplifiers are all RCA, but I replaced them fooling around one day.  The originals are Magnavox branded, coded 274-5943.  All 16 of the 6V6 output tubes are Magnavox branded, coded 210-5943.  The 5Y3GT rectifier in the radio power supply chassis is coded 274-5943.  The 6CM7 in the Phantom Control chassis is coded 274-5948.  The 6X4 rectifier is not coded that I could see, but the font looks like Sylvania to me.  I could not conveniently remove tubes in the radio chassis, so those will have to wait until I get that chassis out.  From an earlier investigation, I found that many of the radio chassis tubes say "made in Great Britain,"

Referring to the code chart I linked, the "210" code is for CBS-Hytron and the "274" code is for RCA.  The "5943" code would indicate that those tube are dated the 43rd week of 1959, and the "5948" tubes would be dated for the 48th week of 1959.  Sometime in October and November of 1959.  This instrument was advertised as being an "early serial number" 1959.  No way would an early serial number 1959 have been built around Christmas time in 1959, by the date codes on the tubes.  Maybe I have a 1960 Concert Grand?  We have to remember that in spite of efforts to the contrary, Magnavox did not sell its instruments by specific model year, but rather by series.  So I have a Magnavox instrument, in the Concert Grand series with tubes dated October and November of 1959.  I have a 1959-ish, but really more a 1960-ish instrument.  I have no idea, and always wondered, how the knuckle dragger who sold me this instrument could tell an early serial number from anything else.  I don't know of any documentation that deciphers serial numbers on Magnavox instruments.  There is also a sticker on the back of the cabinet that says "Copyright 1959".  Assuming this is a 1959 model, possibly sold late in 1958 (remember the "early serial number") that sticker would be a tad precipitous, wouldn't it?  

Pictures:

The business end of a Concert Grand



The 8201 Channel 1 amplifier



Properly phased Channel 1 bass speaker.



One of the 16 6V6 output tubes.



RCA-supplied 5Y3 GT radio chassis rectifier.



Typical RCA "stop sign" font on the 5Y3GT.



This instrument is loaded with clear-top tubes. It is really pretty watching this thing run with the light off. Very sparkly.


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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by jerryhawthorne on Tue Jun 02, 2015 6:30 pm

You know WC your are just crazy but that thing is a beast and based on that should just sound great. More power to you and I will be watching! This puts another level over post war Scotts. At least you don't have pot metal in there like my FADA 46. This should be a fun experience and the chassis look really clean. It would only take me two years to go through that thing but it would be fun. Keep on plugging away.
Best, Jerry

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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by Bill Cahill on Tue Jun 02, 2015 6:40 pm

For me it would be a three year project. I'd recommend you take your time. Part placement is critical. It is a '60 model.
I'm worried enough with my latest ten tube radio with electric tuning.

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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by jerryhawthorne on Tue Jun 02, 2015 6:52 pm

Bill, let us all track WC and confuse him as much as we can. It may take him 3 years!
Best to all, Jerry

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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by 75X11 on Tue Jun 02, 2015 7:24 pm

I imagine WC's fun filter is set on confusion reject when working around these furniture powerhouses.
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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by Wildcat445 on Wed Jun 03, 2015 1:11 am

I will have to admit that this project is somewhat daunting.  I have never worked on anything with this many parts before.  I have planned, studied, looked at the schematic until my eyeballs bugged out, all with the idea of not making any mistakes.  I believe my course of action will include preliminary measurements of resistors and that, making sure I have everything I need so as not to hold up the project unnecessarily.  I will do one amp chassis then fire the thing up and make sure I have not made it worse.  Or that I don't let out the magic smoke.  Then the Channel 2 amp similarly.  Then the power supply for the radio chassis.  Then the radio chassis, which will be ten times more work than both amp chassis combined.  Then I'm going to see if the Phantom Control works.  If it does, I will probably be running out of summer by that time.  I may leave it as is, or wait until next year to dig into that system.  The changer is done with the exception of needing a needle and the drive tire replaced.  This contraption is the sexiest piece of electronic equipment I have ever seen.  I'm excited to see how it works when I'm done.

I have obtained a Multiplex adapter (MPX) for this instrument.  Factory documentation says to mount the MPX adapter onto the back cover for the cabinet.  That arrangement seems horribly ungainly to me.  It would be a nightmare to remove the back for whatever reason.  The instrument could not be operated with the back off and with the MPX adapter disconnected.  So I have come up with another idea.  What about if I build a shelf much like the power supply for the radio chassis sits on.  Mount this shelf above the radio power supply chassis.  There should be sufficient room between that chassis and the bottom of the record changer compartment.  I have a piece of hardwood, I believe it to be ash, that I could machine the edges on and stain it and make it look nice, like the rest of the inside of the cabinet.  This arrangement will obstruct my vision of the radio chassis, but with the back on, that should not be an issue.  There should be room to manage the jumble of wiring adding the MPX will create.  

I appreciate you guys following along. I want us to have fun with this project. Jump in with your suggestions and comments. You might have THE TIP that will stand this project in good stead. I want this instrument to operate for another 50 years.

WC

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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by Conelrad on Wed Jun 03, 2015 1:35 am

Too bad 5V6GT's won't do (600mA heater), I know where a stash of them is.

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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by Bill Cahill on Wed Jun 03, 2015 7:03 am

Those are for series string TV's. More filament current doesn't make for more audio power. In fact, they didn't put out as much. About equal to 25L6.

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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by Conelrad on Wed Jun 03, 2015 12:18 pm

Not to pick at details, but my Tung-Sol book shows almost identical characteristics for audio, including 285V/92mA/14W in PP AB1, filament notwithstanding.

Better than no tubes at all......

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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by 75X11 on Wed Jun 03, 2015 5:33 pm

How large is the MPX unit?
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Re: Restoration of a Magnavox Concert Grand model 1ST800F

Post by jerryhawthorne on Wed Jun 03, 2015 5:42 pm

Come on WC and get to fixing the radio so we can confuse you. Looking forward to your progress.
Jerry

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Re: Restoration of a Magnavox Concert Grand model 1ST800F

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