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 Post subject: V-M Model 700 Tape Recorder Restored, VU Meter Question
PostPosted: Apr Wed 08, 2020 8:46 pm 
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It only took four years, but I finally finished up restoration of a Voice of Music Model 700 tape recorder. The Model 700 is V-M's first tape recorder, and the build date on this one is April, 1955. I bought this machine off EBay in November, 2015.

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VM700n.jpg
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In December, 2015, I completely disassembled the recorder, and replaced all the wax/paper caps, electrolytics, and several resistors.

Here is a view of the underside of the electrical chassis with original components:

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VM700j.jpg
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A 300 ohm sand resistor was mostly sand in the bottom of the chassis:

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VM700i.jpg
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VM700k.jpg
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I also ordered new belts and idler and capstan drive wheels from Gary Stork at Voice of Music. However, I put the project aside for the holidays, and somehow, just never got back to it. But it kept nagging at me, but the more time went by, the more I resisted getting back to it.

When the stay at home orders came out a few weeks ago, I decided to finish up this project. So I pulled everything out of the storage closet, and re-read the manuals to refresh my memory. I could not remember at first what some of the various parts and screws were, but it eventually all came back (hmm, dementia not too bad, yet)

I installed the new belts, the new idler wheel and capstan drive wheel. And replaced the pilot light with a new #47 bulb, and the recording and distortion indicator lamps with new #51 bulbs as the originals tested bad (more about that later).

I was working through the lubrication instructions that Gary provided with the rubber kit, and noticed that a major part, the take up rod that actuates the rewind function, was missing.

I looked all over for it, but couldn't find, and didn't think I would have removed it anyway. So I looked at my tear-down photos, and it was missing when I disassembled the machine. Fortunately, Gary had a replacement (he has lots of them, actually), and a few days later, I was able to complete assembling the machine.

Before putting the unit back in the cabinet, I decided to check it out. Of course, it didn't work right. As soon as it was turned on, it started in fast forward mode. Disgusted, I shut it off, the spent the rest of the day and night studying the service manual.

Resigned to tearing it back down again, the next day I pulled the mechanical top off the electrical chassis and flipped it over, and immediately saw I had routed one of the belts on the wrong side of the idler pulley. I corrected that, put everything back together, and problem solved!

Next, I decided to test the amplifier. I had some old family tapes and I put one on. Unfortunately, those old tapes were all old 4 track tapes, but I could tell the amp was working. I did a quick test with a microphone, and all sounded good.

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VM700o.jpg
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Then I fed a signal from a turntable and recorded a track. That came out ok, but remember those new #51 bulbs I put in? They weren't working. So I looked at the schematic to see what the problem might be, and noticed that those bulbs are not #51 bulbs, they are NE51 bulbs. So I dug the originals out of the trash and put them back in, and guess what? They work just fine.

Although I have the unit back in the case, and the machine is functioning as it should, there seems to be some mechanical noise that comes and goes when it is running, and I need to track that down. Maybe in four years :roll:

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VM700p.jpg
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You can see a short clip at this link:

https://www.dropbox.com/s/c0y2q1c63mph3lq/IMG_1289.MOV?dl=0

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 Post subject: Re: V-M Model 700 Tape Recorder Restored
PostPosted: Apr Wed 08, 2020 9:27 pm 
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Very nice, Ed. Your post brought back fond memories of fooling around with my Dad's V-M 722 recorder.

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Last edited by stevebyan on Apr Thu 09, 2020 3:01 am, edited 1 time in total.

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 Post subject: Re: V-M Model 700 Tape Recorder Restored
PostPosted: Apr Wed 08, 2020 9:35 pm 
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Location: Urbana, Illinois
The high school I attended in the mid 1960’s owned at least one of this model. I was a member of the school’s “Audio Visual Club.” We assisted the teachers and staff with providing projectors (both 16mm movie film and film-strip), sound equipment, record players, and tape recorders. I recall tearing down one of these VM tape recorders to replace a loose belt and give it some lubrication. My repair was successful.

-EB

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 Post subject: Re: V-M Model 700 Tape Recorder Restored
PostPosted: Apr Thu 09, 2020 12:37 am 
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Wow, how nice!

Larry

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 Post subject: Using an External Recording/VU Meter When Taping
PostPosted: Apr Thu 09, 2020 1:29 pm 
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The instructions that came with my V-M Model 700 tape recorder make reference to being able to use an external meter to monitor the recording level. The meter would be plugged in one of the external speaker jacks (see detail, below).

I'm assuming the meter measures the voltage at the speaker jack, but does anyone know what kind of meter would have been used back then?

If one knew the peak voltage at which distortion would occur, I suppose an analog VOM or even an oscilloscope could be used, but without that knowledge, I'm not sure that would be any more helpful than the flickering distort light on the recorder.

Is it possible that a VU meter could be used externally through this connection? Being able to adjust the recording level with a real VU meter in the manner described below would be very helpful.

Attachment:
Ext_Meter.jpg
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 Post subject: Re: Using an External Recording/VU Meter When Taping
PostPosted: Apr Thu 09, 2020 2:47 pm 
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Need to see how that jack #2 is placed in the circuit to answer better.


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 Post subject: Re: Using an External Recording/VU Meter When Taping
PostPosted: Apr Thu 09, 2020 2:55 pm 
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Whatever you connect to the speaker terminal on the V-M 700, you will need to calibrate it to the recording level on the tape, with the amount of headroom you want. You'll either need something with multiple ranges, like a VOM or AC VTVM, or an attenuator in front of a true 600Ω line VU meter, or a diode bridge feeding a pot in series with a milliammeter or microammeter that has a VU scale.

You'll need to establish a standardized volume control setting on the V-M 700 as well. You might consider re-wiring the connector to tap into the record amplifier, or at the top of the volume control on the playback amp, so the level won't be dependent on the playback volume level.

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 Post subject: Re: Using an External Recording/VU Meter When Taping
PostPosted: Apr Thu 09, 2020 2:59 pm 
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Was the meter they mention supplied as an accessory? If so, it would have been factory calibrated. If it is a "standard" VU meter, it will need to be impedance matched and calibrated to the recorder.

It is interesting that they want you to use the jack that keeps the internal speaker on while recording. Doesn't seem right.

On this machine, the "volume" control functions as both the record level and playback volume control. I used one of these machines in the "AV Club" in high school. I recall that the flickering neon record level bulb introduced tits own distortion into the recording which could be heard while monitoring with the speaker. It sounded best when the bulb was removed.

Dave


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 Post subject: Re: V-M Model 700 Tape Recorder Restored, VU Meter Question
PostPosted: Apr Thu 09, 2020 3:35 pm 
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Tbirdkid, schematic detail below.

Steve, thanks. I was hoping for a play and plug solution :roll: I guess if I had a schematic, I could figure it out.

Dave, I have not seen any mention of the meter being supplied as an accessory. The only reference is what I highlighted above. I could check and see if Gary of V-M knows. I suppose it was assumed if you were smart enough to buy one of these in 1955, you could figure out what kind of meter to use.

I think the reason for using Speaker #2 is that if #1 is cut out, you can't monitor the recording. If the meter were plugged into Speaker #1, you would lose audio.

The distort light is very hard to see, not because it is dim, but just not well designed and my eyes aren't that great. I haven't had time to do a lot of experimenting with recording levels yet, but since there are no markings on the volume control knob, there's not even a visual reference point.

I think I might make a dial scale on some acetate and put it under the volume knob to have some kind of constant reference point.

Attachment:
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SchmDetail_2.jpg [ 227.54 KiB | Viewed 619 times ]

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 Post subject: Re: V-M Model 700 Tape Recorder Restored, VU Meter Question
PostPosted: Apr Thu 09, 2020 3:47 pm 
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Ed Morris wrote:
I think the reason for using Speaker #2 is that if #1 is cut out, you can't monitor the recording. If the meter were plugged into Speaker #1, you would lose audio.
But if the "Monitor" switch is on, Jack 1 will drive the meter with the internal speaker off. Recordings with these types of machines are usually done with the internal speaker turned off to avoid feedback when a microphone is used. I guess it could be used either way.

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 Post subject: Re: V-M Model 700 Tape Recorder Restored, VU Meter Question
PostPosted: Apr Thu 09, 2020 3:58 pm 
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True, but I doubt I would ever make a live recording with a mic. I would be recording a few record albums from a turntable with the signal fed into the magnetic phono input, so monitoring through the internal speaker during recording is useful.

I could also record from the tape out of a hi-fi system, in which case I wouldn't need to monitor through the recorder, and I might end up going that way.

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 Post subject: Re: V-M Model 700 Tape Recorder Restored, VU Meter Question
PostPosted: Apr Fri 10, 2020 2:27 am 
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VU meters come with a 3600 ohm resistor. Try the VM meter in series the
the grounded end of C36. Then the calibration control will be the treble pot.
Attachment:
vm vu.JPG
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 Post subject: Re: V-M Model 700 Tape Recorder Restored, VU Meter Question
PostPosted: Apr Fri 10, 2020 12:31 pm 
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Thanks to all for comments. I'm keeping notes on all the suggestions. Everything is working well, so I'm not anxious to pull the chassis back out yet.

I did hook up a VOM to the Speaker 2 outlet. On playback on a tape I recorded previously, an Artie Shaw album, the average voltage reading on the 2.5 volt AC scale rarely got above .5 volts.

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VM700t.jpg
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Attachment:
VM700s.jpg
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I made a dial scale template so I would have some point of reference to set a recording level. Then I taped Tommy Dorsey album with the setting at the red arrow in the image below, which gave a peak voltage of about .5 volts when recording. On this particular album, that seemed to be a good recording level setting.

Attachment:
VM700r.jpg
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I think setting the level between the 3rd large tick mark (red arrow) and the mid setting would work for most recordings, depending on the type of music.

I will keep an eye out for a VU meter I can experiment with and try out some of the suggestions offered here.

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 Post subject: Re: V-M Model 700 Tape Recorder Restored, VU Meter Question
PostPosted: Apr Fri 10, 2020 1:07 pm 
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Your Simpson can give you a voltage indication, probably average peak, but if you want to track an actual recording level, you'll really need a VU meter. They have ballistics that both correspond to actual recording standards, and respond properly to high peaks and lows so you can see what you are actually recording. I'd think the Simpson would be too sluggish to give you a true indication of any peak readings.

For a sine wave, the Simpson is just fine. For music or voice, not so much.

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 Post subject: Re: V-M Model 700 Tape Recorder Restored, VU Meter Question
PostPosted: Apr Fri 10, 2020 2:35 pm 
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Nice to see one of those restored! I have one in the Restoration Pile; a slightly later model which has a 6E5 as a level indicator.

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 Post subject: Re: V-M Model 700 Tape Recorder Restored, VU Meter Question
PostPosted: Apr Fri 10, 2020 2:44 pm 
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Thanks, Tim. Have you got your belts and wheels from Voice of Music yet? You can order a kit from Gary. Mine sat around for four years, but I had everything I needed when I finally got motivated. The kit I received had the service manual and Gary's step by step instructions for installing the new belts and wheels. He really appreciates it when these tape recorders are restored.

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 Post subject: Re: V-M Model 700 Tape Recorder Restored, VU Meter Question
PostPosted: Apr Fri 10, 2020 3:06 pm 
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No, not just yet; I have too many projects ahead of it. Mine came from a local flea market; I couldn't pass it up, as I used one as a teenager. It still has an ID tag on it from the Beaver Falls school system!

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 Post subject: Re: V-M Model 700 Tape Recorder Restored, VU Meter Question
PostPosted: Apr Fri 10, 2020 5:32 pm 
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Tim Tress wrote:
No, not just yet; I have too many projects ahead of it. Mine came from a local flea market; I couldn't pass it up, as I used one as a teenager. It still has an ID tag on it from the Beaver Falls school system!
The two of us must be roughly the same "vintage" ourselves? (I'm 70 myself).

I was fascinated by tape recorders as a teenager. The high school I attended had a VM 700.

My high school also had a gigantic Sony "stereo tape recorder" which was kept in the school's library. The school library had an entire shelf of popular and classical music on 7" reels. I recall listening to a stereo tape of the sound track from the film "Goldfinger" (1964) through a pair of really good headphones. I hadn't heard much actual "stereo" before that. Those reel-reel tapes sold by the major record labels sounded far better than the average 12" LP record of that era. I liked the total absence of "tick and scratch" noises in the background. I didn't really mind a bit of tape hiss! Plus, those headphones sounded far better than most of the speaker systems of the day.

That was quite the "transformative" experience for me. It made me aware of the huge difference in audio quality between a pocket transistor radio vs. a real "Hi-Fi" audio system.

-EB

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 Post subject: Re: V-M Model 700 Tape Recorder Restored, VU Meter Question
PostPosted: Apr Fri 10, 2020 6:54 pm 
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I have repaired many of those machines. In Canada they were marketed,
under the brand ' Sea Breeze'. Schools had them as the centre piece of a cart
wheeled AV system.

One place I worked for had those and Webcors as rental machines, few dollars
a day.
I have a few at one of my places now. I think the heads are worn, and
likely decks lube frozen.

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 Post subject: Re: V-M Model 700 Tape Recorder Restored, VU Meter Question
PostPosted: Apr Fri 10, 2020 7:42 pm 
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I have a VM model 730 Tape-O-Matic that I need to get to one of these days. I believe mine is a 1961 model. It has an eye tube. All the pressure pads for the tape transport are missing on mine.

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