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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc. |
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12th Jan 2021, 10:32 pm | #141 |
Octode
Join Date: Sep 2017
Location: Bristol, UK.
Posts: 1,642
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Re: Grundig TK20 and Truvox R82. Help Required Please.
Thanks, It hadn't occured to me that there is an effect from the core material. I now feel illuminated!
Mike |
12th Jan 2021, 10:50 pm | #142 |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
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Re: Grundig TK20 and Truvox R82. Help Required Please.
1.25H (1,250mH) seemed high to me. The DC resistance of 1,100 Ohms also is higher than what I am used to, so maybe the two go hand in hand in this case.
David |
14th Jan 2021, 12:57 pm | #143 |
Pentode
Join Date: Mar 2013
Location: Liverpool
Posts: 102
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Re: Grundig TK20 and Truvox R82. Help Required Please.
Good morning all, after having fixed the hum on the Truvox R82 caused by the open circuit head, I now seem to have another problem. The main capstan motor runs fine at 3.75ips but is a trifle slow at 7.5ips and also from time to time it grinds to a halt and then will either pick up again itself or with a spin of the reels gets it going again. I've read some of the service notes which mention to two large 3k and 4k wire wound resistors. The circuit diagram for the capstan motor shows three wires red, yellow and green, or red, yellow and mauve depending on which diagram you look at. Problem is I can only see two black wires connected to the motor from the resistors and that's it. It mentions a 2uF capacitor, but I can't see that either! Problem is that this is intermittent which makes it hard to pinpoint the cause.
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14th Jan 2021, 1:24 pm | #144 |
Octode
Join Date: Jul 2006
Location: Perth, Western Australia
Posts: 1,965
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Re: Grundig TK20 and Truvox R82. Help Required Please.
Ted, I always understood it as the opposite: the record heads have a lower inductance (and impedance at the nominal frequency) relative to play heads.
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14th Jan 2021, 3:10 pm | #145 | |
Octode
Join Date: Sep 2017
Location: Bristol, UK.
Posts: 1,642
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Re: Grundig TK20 and Truvox R82. Help Required Please.
Quote:
BRENELL (BOGEN) TAPE HEADS (From: “Tape Recorder” magazine, September 1967, article ‘Tape Recorder Service’, HW Hellyer) Recording head UK202, 2/2 track Inductance - 120mH Impedance at 1kHz – 780 Ω DC resistance – 75 Ω Bias at 100kHz - 23V at 1mA Recording current (3-75 ips) - 120μA Output at 2kHz (3.75 ips) – 2.4mV Replay head UK200, 2/2 track. Inductance - 550mH Impedance - 3.5KΩ DC resistance – 300Ω Bias (1OOkHz) - 70V at 0.8mA Record current - 50μA Output at 2kHz (3 ips) - 5.8mV. Erase head BL210, 2/2 track Inductance - 2mH Erase current - 55μA Erase voltage - 80V @ 100kHz [Note: with appropriate circuitry, the UK202 and UK200 heads can also both be used as record/playback heads] |
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14th Jan 2021, 3:27 pm | #146 | |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
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Re: Grundig TK20 and Truvox R82. Help Required Please.
Quote:
I can only assume that your R82 is not a full Mk. 2 (as referenced before) and its capstan motor is not the type that requires a Run capacitor, i.e. it probably is a Shaded Pole motor and hence only 2 connections. David |
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14th Jan 2021, 4:52 pm | #147 |
Pentode
Join Date: Mar 2013
Location: Liverpool
Posts: 102
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Re: Grundig TK20 and Truvox R82. Help Required Please.
I think you're probably right regarding the Mk2 thing. Even the head assembly is totally different to the later version. Assuming we're right about the motor then, how is the speed controlled, or is the motor a constant speed one? I assume it is because it has a stepped pinion on to which one of two idler wheels contacts depending on the speed selected. If the motor varies its speed is this likely to be motor fault, which of course would mean a lot of dismantling which I think is out of the question, even assuming I could get a motor! There's something not right with those wire wound resistors too; they're listed as 3k and 4k but when I measured them they were only 400ohm! I'll double check that though!
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14th Jan 2021, 5:24 pm | #148 |
Pentode
Join Date: Mar 2013
Location: Liverpool
Posts: 102
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Re: Grundig TK20 and Truvox R82. Help Required Please.
UPDATE. I think you are definitely right. The answer is in the first couple a paragraphs of Tape Recorder magazine article I posted from 1963. It also shows the resistors to be 500ohm & 700ohm which is more in keeping with the measures I got. The diagrams are also the same as mine too.
Maybe it would be worth checking the connections as they recommend and re-soldering just in case there is a dry joint. |
14th Jan 2021, 6:22 pm | #149 |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
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Re: Grundig TK20 and Truvox R82. Help Required Please.
Well spotted. As these are probably large wirewound resistors they may have their values written on them.
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14th Jan 2021, 8:24 pm | #150 |
Pentode
Join Date: Mar 2013
Location: Liverpool
Posts: 102
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Re: Grundig TK20 and Truvox R82. Help Required Please.
The resistor connected to the motor reads 450 ohm, the other reads 434 ohms. R1 matches but R2 according to the diagram should read 700 ohms. Not sure if R2 would affect the capstan motor though, but it does say that these two resistors can lead to erratic transport action by either poor connection or the heat they generate.
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14th Jan 2021, 8:39 pm | #151 |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
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Re: Grundig TK20 and Truvox R82. Help Required Please.
As far as I can see R2 will not affect the capstan motor.
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14th Jan 2021, 8:55 pm | #152 |
Pentode
Join Date: Mar 2013
Location: Liverpool
Posts: 102
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Re: Grundig TK20 and Truvox R82. Help Required Please.
I didn't think so. What about C5 the 0.01 cap on the speed change switch when set at 7.5ips as in the schematic?
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14th Jan 2021, 9:21 pm | #153 |
Pentode
Join Date: Mar 2013
Location: Liverpool
Posts: 102
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Re: Grundig TK20 and Truvox R82. Help Required Please.
Here's pic of the type of motor on the Truvox as the capstan motor. Is this what they are referring to when they say a Hoover motor! It's described as a Papst, external rotor, hysteresis motor apparently.
Last edited by TerryB44; 14th Jan 2021 at 9:28 pm. |
14th Jan 2021, 9:43 pm | #154 |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
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Re: Grundig TK20 and Truvox R82. Help Required Please.
C5 is just for equalisation, nothing to do with motor control.
Is it definitely the motor that is struggling at 7.5 ips or could the motor be OK but the capstan is struggling due to drive idler ? |
14th Jan 2021, 10:52 pm | #155 |
Pentode
Join Date: Mar 2013
Location: Liverpool
Posts: 102
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Re: Grundig TK20 and Truvox R82. Help Required Please.
Ok. The sequence is the motor has a stepped pinion which engages with the idler wheels and the idler wheels then turn the flywheel which has the capstan on it. I've cleaned everything as best I can but at 7.5ips it runs slow and sometimes the whole system slows down including motor and will pick up after a bit or sometimes with a bit of help by rotating the reels by hand. Because it's intermeittent it's difficult to pin point the cause.
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15th Jan 2021, 12:51 am | #156 | |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
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Re: Grundig TK20 and Truvox R82. Help Required Please.
Quote:
I am surprised that you have the Papst BP1303B (is your motor the same as the Brenell photo ?) because I didn't think the Papst is a shaded pole motor and thought previously your lack of a run capacitor could be explained by the capstan motor being a shaded pole motor ? |
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15th Jan 2021, 1:20 am | #157 |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
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Re: Grundig TK20 and Truvox R82. Help Required Please.
Just realized that the Brenell motor photo is not a Papst motor but AEI but once again not a shaded pole motor as far as I know ?
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15th Jan 2021, 11:55 am | #158 |
Pentode
Join Date: Mar 2013
Location: Liverpool
Posts: 102
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Re: Grundig TK20 and Truvox R82. Help Required Please.
Good morning David, I've had a look at my motors and the capstan drive motor is definitely the same as the one in the Brenell pic. Picture of mine is below. The rewind and take up motors are both AEI so perhaps its no surprise that the capstan one would be too. I can't see any markings on the capstan motor either. I'm going to re-solder all the joints at those big resistors just in case there's a bad connection somewhere.
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15th Jan 2021, 12:26 pm | #159 |
Pentode
Join Date: Mar 2013
Location: Liverpool
Posts: 102
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Re: Grundig TK20 and Truvox R82. Help Required Please.
I've just found a manual on line for the Brenell Mk5 which says it uses two shaded pole motors for rewind and take up which are the ones that look like my capstan motor, so maybe it is a shaded pole motor after all.
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15th Jan 2021, 12:45 pm | #160 |
Pentode
Join Date: Mar 2013
Location: Liverpool
Posts: 102
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Re: Grundig TK20 and Truvox R82. Help Required Please.
Here's a pic from the Brenell manual.
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