Fundamentally, the main differences in the amp on record and playback is that bass boost is switched in on playback and treble boost switched in on record. Because the switching mechanism is so complex on the Grundigs it is worth paying attention to this to look for failure, as dhaen as suggested.
On the TK60 model, a single EM84 is used, even though it is a stereo model. Seperate indicators for the levels on each channel were not widely used by Grundig until meters replaced magic eyes. On further investigation a version of the TK60 called the TM60 was released, which had the pre-amps and equilisation but not the power amp stages (1 x ECC83, 2 x EL84), and it was designed for use with suitable stereo amps. I suspect that the deck Duo has is this model, and hopefully the schematic will confirm it.
dhaen said:
On the TK60 model, a single EM84 is used, even though it is a stereo model. Seperate indicators for the levels on each channel were not widely used by Grundig until meters replaced magic eyes. On further investigation a version of the TK60 called the TM60 was released, which had the pre-amps and equilisation but not the power amp stages (1 x ECC83, 2 x EL84), and it was designed for use with suitable stereo amps. I suspect that the deck Duo has is this model, and hopefully the schematic will confirm it.
Yes, this recorder has no power amps. Just preamp and eq tubes.
BTW, what should be the signal amplitude at the record head input at a normal recording level?
I found a problem with the recording switch relay and fixed that. I cleaned and calibrated and tested all the relays in the unit so I know they are working fine.
I now get a signal at the recording head in record mode, but it's very distorted and I don't know how much amplitude it should have.
BTW, what should be the signal amplitude at the record head input at a normal recording level?
I found a problem with the recording switch relay and fixed that. I cleaned and calibrated and tested all the relays in the unit so I know they are working fine.
I now get a signal at the recording head in record mode, but it's very distorted and I don't know how much amplitude it should have.
Duo,
I can't remember the signal amplitude to the record head of this kind of deck. I would guess 20 volts or so would make a recording, but what you have to remember is that it will use AC bias. That means that you should see the audio, amplitude modulated on a superisonic carrier. If the bias is missing, you will make low very distorted recordings.
Cheers,
I can't remember the signal amplitude to the record head of this kind of deck. I would guess 20 volts or so would make a recording, but what you have to remember is that it will use AC bias. That means that you should see the audio, amplitude modulated on a superisonic carrier. If the bias is missing, you will make low very distorted recordings.
Cheers,
Where is a good source in Canada to get capacitors for this recorder? I want to replace all the axial caps.
I also found that the ECC81 tubes are a bit gassy. I'll look into trying better replacements to see what happens.
I think the record bias oscillator may be working, it's just that the voltage at the head if very weak for audio.
I found that the distortion is coming from the first half of the ECC81's. The EF86 stages are fine, and the output stages of the ECC81's are fine. Can anyone suggest parts other than caps to check to fix that distortion problem? I tested all the resistors and they are okay.
I also found that the ECC81 tubes are a bit gassy. I'll look into trying better replacements to see what happens.
I think the record bias oscillator may be working, it's just that the voltage at the head if very weak for audio.
I found that the distortion is coming from the first half of the ECC81's. The EF86 stages are fine, and the output stages of the ECC81's are fine. Can anyone suggest parts other than caps to check to fix that distortion problem? I tested all the resistors and they are okay.
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Duo said:
The EL95 is used for the oscillator.
While not ruling out leaky caps or shorted cathode electrolytics for the cause of distortion in the first stages of the ECC81s it seems a bit fortuitous that both channels would have developed the same fault at the same time....
What appears strange to me is that if the deck is a TM60 it should have two EL95s, one for the oscillator and one for bias. Your deck has one EL95 and the symptoms of a lack of bias...I am wondering whether a previous owner has removed one EL95 (for whatever reason) and attempted to use the other to provide bias as well as erase?
Thinking aloud....
We have already established that this is not a regular model, as it has no power amplifers. It may well have other variations such as a single oscillator.
Certainly the symptoms suggest no bias. On the other hand Duo clearly stated that it erases.
And, the fault is on both channels....we assume... Has Duo actually checked both?
Or, maybe it's switching problems after all. Indeed the bias is applied to the bottom side (on the schematic) of the record head. This point is grounded in playback. Now, if the switch was still closed in record....
BTW I've now got the TK35 schematics from Frank.
We have already established that this is not a regular model, as it has no power amplifers. It may well have other variations such as a single oscillator.
Certainly the symptoms suggest no bias. On the other hand Duo clearly stated that it erases.
And, the fault is on both channels....we assume... Has Duo actually checked both?
Or, maybe it's switching problems after all. Indeed the bias is applied to the bottom side (on the schematic) of the record head. This point is grounded in playback. Now, if the switch was still closed in record....
BTW I've now got the TK35 schematics from Frank.
John,
The TM60 is the Grundig stereo deck without output amps, designed to run through a stereo amp and fit into a console, which Duo retrieved it from - that's why I assumed it is more likely to be a TM60 rather than be based on a mono TK35, but obviously this is pure guesswork.
However, the EF86/ECC81 stages are virtually identical for both recorders, duplicated for stereo of course, although the network for treble boost on record and bass boost on playback are different. If Duo's deck has just the one EL95, it is likely to be the same as the TK35.
The TM60 is the Grundig stereo deck without output amps, designed to run through a stereo amp and fit into a console, which Duo retrieved it from - that's why I assumed it is more likely to be a TM60 rather than be based on a mono TK35, but obviously this is pure guesswork.
However, the EF86/ECC81 stages are virtually identical for both recorders, duplicated for stereo of course, although the network for treble boost on record and bass boost on playback are different. If Duo's deck has just the one EL95, it is likely to be the same as the TK35.
Duo,
As the pre-amps in the TK35 and TK/TM60 are very similar there's not a problem, but if you look at:
http://www.heinffm.de/0199d992c41241201/0199d992da1184701/0199d992da1186204/0199d992da12ad00e.html
...you can see that the basic deck used in the TK/TM60 is also the same as the TK35. Is your deck a two speed or three speed model?
As the pre-amps in the TK35 and TK/TM60 are very similar there's not a problem, but if you look at:
http://www.heinffm.de/0199d992c41241201/0199d992da1184701/0199d992da1186204/0199d992da12ad00e.html
...you can see that the basic deck used in the TK/TM60 is also the same as the TK35. Is your deck a two speed or three speed model?
HI,
Because the schematics are too large to post, I've put it on my server. Here is the link:
TK35 revised
And now to try and embed the pix...
Hope this works!
edit: took off dupicate
Because the schematics are too large to post, I've put it on my server. Here is the link:
TK35 revised
And now to try and embed the pix...
Hope this works!
An externally hosted image should be here but it was not working when we last tested it.
edit: took off dupicate
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