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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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Old 16th Nov 2018, 12:07 pm   #21
NorfolkDaveUK
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Default Re: Using a meter for calibration .

Great thats what I thought , holy smokes I get it ..haha .

Many thanks Lawrence .
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Old 16th Nov 2018, 12:32 pm   #22
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Default Re: Using a meter for calibration .

I`m having a bit of an issue setting the record level . I did the bias at 1khz and went down 3.5dB which is my amount of choice seems to work for me . The problem I have now is that I can`t get the record level to adjust up far enough . Once side is worse than the other , one just about makes it to 0dB with the pot wound fully open , the other side is way off . The signal coming in seems to be identical . So I guess something on the record card is still amiss ....swings and roundabouts this game init .lol
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Old 16th Nov 2018, 12:45 pm   #23
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Default Re: Using a meter for calibration .

No, for 4dB (or whatever) down after peak the bias is set with 10kHz @ -20dB input, not 1kHz, typically 1kHz would be about 0.5dB down after peak.

Lawrence.
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Old 16th Nov 2018, 12:49 pm   #24
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Default Re: Using a meter for calibration .

Ahhh ok ......ok ...let me try that again ..thanks .. I tried to follow the manual , but i couldn't find a peak , so i tried to do it as per the A77 ...ok ..lets have another go ...thanks Lawrence..
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Old 16th Nov 2018, 1:28 pm   #25
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Default Re: Using a meter for calibration .

Well I`m still having the same issue on the left side but after re-doing the adjustments , it is a now fine on the right side .

I`ve just checked the Seimens with the scope and it is a bit out of calibration . Its reading 0dB at 2.26v (peak to peak) so its about half a volt , peak to peak out so I will have to somehow calibrate it but I can`t find a manual at the moment . I`m having the same issue with the left hand record though , the tape is an unused basf so its not the tape , the heads are clean and dmag`d its not that . Any ideas where I might look . Just thought I would ask in case you know save me going round the trees ....ta
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Old 16th Nov 2018, 1:33 pm   #26
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Default Re: Using a meter for calibration .

Looking at your meter photo's have you set the meter zero since, make sure the meter needle isn't bent.

Lawrence.
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Old 16th Nov 2018, 1:34 pm   #27
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Default Re: Using a meter for calibration .

2.26V p-p isn't far out.

0.775*2*1.414 = 2.2V
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Old 16th Nov 2018, 1:42 pm   #28
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Default Re: Using a meter for calibration .

Thanks station !! I thoght it was more than that , thanks for the equation !

Lawrence ....I will set the zero and start the process again if it needs it . I set it before I started , but I`ll check it and see . The right side is spot on though , so I have to assume its the machine not the meter though right ? I haven`t touched the meter between left and right. ....the bias traps are also much different (although in spec)
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Old 16th Nov 2018, 1:49 pm   #29
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Default Re: Using a meter for calibration .

Ref. post#26: By set zero I was meaning the meter needle's resting point eg: 0 on the voltage scale with no input, it looks to be out on the photo's.

Lawrence.

Last edited by ms660; 16th Nov 2018 at 1:55 pm. Reason: post ref added
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Old 16th Nov 2018, 1:56 pm   #30
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Default Re: Using a meter for calibration .

ok . measures a signal from the sig gen on the scope @ 2.2v p 2 p , fed that into the meter and its bang on the money , so the meter I would say it very accurate. So this must bring me back the the machine its self . The signal coming into the record amp is fine but according to the V.U.`s i cant get the signal on the left to hit 0dB the right is 0dB at about half the pot . The left is at - 1 to -2dB with the pot maxed out . -


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Originally Posted by ms660 View Post

Ref. post#26: By set zero I was meaning the meter needle's resting point eg: 0 on the voltage scale with no input, it looks to be out on the photo's.

Lawrence.
Oh yes ...they were the ebay photos bud . I have set zero
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Old 16th Nov 2018, 2:02 pm   #31
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Default Re: Using a meter for calibration .

by the way the milivoltmeter is agreeing with the VU`s regards the output
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Old 16th Nov 2018, 3:47 pm   #32
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Default Re: Using a meter for calibration .

Can we assume that the levels on both channels are ok when the monitor switch is switched to input?

Lawrence.
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Old 16th Nov 2018, 5:37 pm   #33
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Default Re: Using a meter for calibration .

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Originally Posted by NorfolkDaveUK View Post
Thanks station !! I thoght it was more than that , thanks for the equation !

Lawrence ....I will set the zero and start the process again if it needs it . I set it before I started , but I`ll check it and see . The right side is spot on though , so I have to assume its the machine not the meter though right ? I haven`t touched the meter between left and right. ....the bias traps are also much different (although in spec)
Ref. post#26: By set zero I was meaning the meter needle's resting point eg: 0 on the voltage scale with no input, it looks to be out on the photo's.

Lawrence.
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Can we assume that the levels on both channels are ok when the monitor switch is switched to input?

Lawrence.

Yeah input is good 0dB both left and right and vu`s sitting pretty.
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Old 16th Nov 2018, 6:32 pm   #34
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Default Re: Using a meter for calibration .

I`ll trace the audio through the circuit in a bit and compare sides . Not feeling too well today so need to recharge a bit.
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Old 16th Nov 2018, 7:26 pm   #35
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Default Re: Using a meter for calibration .

Someone (not me ) put q3 in upside down .,...hahah

Now everything is working brilliantly . Thanks again for all your help . A few more with this meter and I`ll be cooking on gas . I have 4 x A77`s here I need to do including a very nice HS model . Should be nice . Let battle commence.
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Old 16th Nov 2018, 9:46 pm   #36
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Default Re: Using a meter for calibration .

Be careful with HS Revoxes. The true originals are good, but they seem to be outnumbered by bodged ones where the motor position is plain wrong or bodged to offset it for the larger diameter capstan. HS means ground zero for frankenstein boxes.

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Old 16th Nov 2018, 10:45 pm   #37
NorfolkDaveUK
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Default Re: Using a meter for calibration .

Quote:
Originally Posted by Radio Wrangler View Post
Be careful with HS Revoxes. The true originals are good, but they seem to be outnumbered by bodged ones where the motor position is plain wrong or bodged to offset it for the larger diameter capstan. HS means ground zero for frankenstein boxes.

David
This one is totally original . Thanks for the warning though .
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Old 17th Nov 2018, 1:34 am   #38
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Default Re: Using a meter for calibration .

Ok just to finish this thread off . Just sailed through the whole calibration process now the machine is debugged and boy it sounds amazing on both record and play . I`m over the moon with the new meter and really can`t wait to get on to the next one which will be a normal A77 . I dont have a calibration tape for 15ips yet so I`ll have to get one for the HS once i get a couple of these out of the door . Thanks everyone for your guidance on the meter, so until next time !
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