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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 12th Oct 2019, 11:59 am   #1
Lef de art
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Default Reel to reel valved tape recorder Geloso G258, problem

Hello my friends.
I have bought recently a almost unused reel to reel tube recorder, Geloso G258.
But I have some problems in the recording mode and it would be a enormous help if someone can share his knowledge.

The recorder It is fully functional in the play mode but while recording the situation starts to change.

The first 10 minutes of recording it records quite nice but after 5 minutes the recording volume and quality are falling and crashing unbelievably. The same things happen and with his erase function while he records.

After 10 minutes you can hear very clear the old recorded sound in the background of the new one. If i turn it off and let it cool for 1 hour and put it back, it does the same thing again. Starts well but it falls after 10 minutes.

I suspect the problem is in capacitors but before I start changing them randomly, I thought maybe someone knows more.
In general I would prefer not to change all the capacitors trying to keep it with its original components.
I also have his electronic diagram for anyone who can read it.
I wish someone could help

Sorry for my bad English
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Old 12th Oct 2019, 12:58 pm   #2
theredhouseinn
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Default Re: Reel to reel valved tape recorder Geloso G258, problem

Hi there.
From your description the bias oscillator is packing up.
You will need to check all capacitors for leakage, preferably with a 20.000 ohms per volt meter like an Avo 8, remember when measuring resistance with an Avo the neg lead is pos for res measurements, important for testing electrolytics. You will also need to test all resistors for tolerance. You must disconnect one end of the component for the measurement.
john.
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Old 12th Oct 2019, 1:01 pm   #3
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Default Re: Reel to reel valved tape recorder Geloso G258, problem

Also make sure that the record/playback switch contacts are clean.

Lawrence.
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Old 12th Oct 2019, 1:02 pm   #4
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Default Re: Reel to reel valved tape recorder Geloso G258, problem

It looks a bit 'Telefunken(ish).

You need to look for any critical paper type capacitors, particularly around the EL95 valve.

Any that go from an anode circuit of a previous stage to the control grid of the next stage. These are 'coupling' capacitors which pass the 'AC' (signal), but block the 'DC'. The basic rule is that if any of these capacitors that has HT on one side, ie, anywhere between 50 and 250 volts DC, it should have close to zero volts DC on the other side. If there's DC voltage on the other side of the capacitor, then it's dangerously leaky and must be replaced. Get your DVM and make these tests - I can spot one, if not two capacitors on that circuit that are likely to be causing your fault.

Edit: Two posts already by other members while I was typing this one.
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Old 12th Oct 2019, 1:12 pm   #5
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Default Re: Reel to reel valved tape recorder Geloso G258, problem

Sorry to have to disagree with post #2, but you can't reliably test capacitors like that. The only way to test for leakage is with their working (or close to it) voltage across them, so do as I say and test them in circuit with the power on and see if there's any DC voltage leaking through them. This only applies to the critical ones operating at HT voltages.
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Old 12th Oct 2019, 2:26 pm   #6
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Default Re: Reel to reel valved tape recorder Geloso G258, problem

Quote:
Originally Posted by Techman View Post
The only way to test for leakage is with their working (or close to it) voltage across them.
I agree absolutely. Capacitors need to be extremely electrically leaky before they'll show up as leaky on a multimeter. You're not measuring resistance, but insulation resistance which is a different thing.

The analogy I use is that it's no use testing a steam boiler designed to work at 150 psi with a 10 psi hydraulic test.
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Old 12th Oct 2019, 6:09 pm   #7
Lef de art
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Default Re: Reel to reel valved tape recorder Geloso G258, problem

Really thanks to all of you for the interest and your messages.
After reading your messages i understand that some capacitors must be replaced otherwise maybe it is dangerous for creating more problems.
Im not that good to reading the diagram but if i understand correct this 7 capacitors i have circle must be replaced?
You think i must change more ?
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Old 12th Oct 2019, 11:03 pm   #8
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Default Re: Reel to reel valved tape recorder Geloso G258, problem

Quote:
Originally Posted by Lef de art View Post
this 7 capacitors i have circle must be replaced?
No, sorry, completely wrong!

I said the paper types. The ones you have circled are all the electrolytic types. The ONLY ONE of these you may need to replace is perhaps the cathode decoupler on the EL95.

You need to re-read my previous post and do the testing as described with your DVM (voltmeter) on the PAPER types and NOT the electrolytic types.

I think that you may be struggling with translating the English.
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Old 13th Oct 2019, 2:07 pm   #9
Lef de art
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Default Re: Reel to reel valved tape recorder Geloso G258, problem

Thanks for the answers and he interest guys.

I will check the paper capacitors with the voltmeter as the techman adviced me and i will inform you for my results.
I have taken some pictures from inside.
To not make any mistake is any way to mark somebody in pictures some paper capacitors ?
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Old 13th Oct 2019, 7:33 pm   #10
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Default Re: Reel to reel valved tape recorder Geloso G258, problem

Might it also be the case that the selenium rectifier(s) are also leaky? If the voltage falls then the bias oscillator will certainly misbehave.
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Old 13th Oct 2019, 10:23 pm   #11
Lef de art
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Default Re: Reel to reel valved tape recorder Geloso G258, problem

Because the problem starts at the recording mode after 5 minutes of use i must test the capacitors in the recording mode and after 5 minutes or doesn't really matter?
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Old 14th Oct 2019, 10:06 am   #12
Lef de art
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Default Re: Reel to reel valved tape recorder Geloso G258, problem

The tape recorder it has 4 tubes.
Two tubes 12AX7
One tube 6AQ5
One tube EM84

There is any chance the problem to be in the 12AX7 ?
The problem occurs after 10 minutes of use. And it is as follows

In the recording mode
1) the quality of the recording goes gradually very low
2) the erase head starts to not erase gradually

In the play mode
1) The moving lines notification of the tube EM84 starts to not move gradually. They lose sensibility .


If i change the position of two 12AX7 can see any difference?
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Old 14th Oct 2019, 7:17 pm   #13
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Default Re: Reel to reel valved tape recorder Geloso G258, problem

Definitely sounds like an hf oscillator problem if both audio and erase are failing. Does the EM84 indicator only lose sensitivity on playback of new recordings (i.e. does it work properly with older recordings)?

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Old 14th Oct 2019, 8:20 pm   #14
Lef de art
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Default Re: Reel to reel valved tape recorder Geloso G258, problem

The EM84 lose sensitivity in both situation. In recording and in playback mode. Does not work correctly with older recordings to.

The tubes i think are ok. They look unused ! I have changed the position in 12AX7 but the situation is the same. After 10 minutes the recording mode dose not work correctly.
The sound of recording gets extremely poor quality.

Is very difficult to measure the capacitors because the top of circuit can't be visible When the upper side of the chassis is placed.
And to be honest i recognise only 2 paper capacitors.
I don't know which fro the others are the paper capacitors
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Old 14th Oct 2019, 8:43 pm   #15
Lef de art
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Default Re: Reel to reel valved tape recorder Geloso G258, problem

I recognise as papper capacitor only the one i have placed in the circle.
The other 1, 2, 3, 4 are papper capacitor ?
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Old 14th Oct 2019, 9:40 pm   #16
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Default Re: Reel to reel valved tape recorder Geloso G258, problem

Can you clarify - in your first post you said "the recorder It is fully functional in the play mode but while recording the situation starts to change". Are you saying that playback sounds OK, but EM84 display is faulty on playback? I think in a recorder of this sort, it would be quite normal for the record level indicator to not be functional (i.e. not to display any signal level) during playback.
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Old 14th Oct 2019, 9:51 pm   #17
Lef de art
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Default Re: Reel to reel valved tape recorder Geloso G258, problem

In the first 10 minutes the EM84 bulb moves correctly in the playback mode and in recording mode.
After this it starts gradually to lose sensitivity . This can be more clear in the playback mode because there it stops completely to move.
In the recording mode continue to move but only with loud sounds in microphone.
I didn't notice any big chance in the sound quality after 10 minutes in the playback mode, with older recordings.

But when is in playback mode after 10 minutes the recording quality gets really bad.
It reminds me the sound of some old transistor recording tapes When the battery was very low.

Sorry for my English
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Old 14th Oct 2019, 9:58 pm   #18
Lef de art
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Default Re: Reel to reel valved tape recorder Geloso G258, problem

In the first 10 minutes the signal indicator of EM84 moves in playback mode and in recording mode when the sound is high.

After 10 minutes the signal indicator lose sensitivity . The recording quality gets bad.
The playback quality does not change I think. But if loose quality then is not really noticeable.

Only the record quality change dramatically.
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Old 14th Oct 2019, 10:32 pm   #19
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Default Re: Reel to reel valved tape recorder Geloso G258, problem

I think you're at the stage where you just have to do some of the voltage checks suggested by Techman earlier in the thread. Watch out for any obvious voltage changes as it gets to the 10-minute point, and look very carefully for any signs of overheating. You will have to do this with power connected, so careful what you touch. To get access to make these readings, you may also have to disconnect the motor to avoid mechanical chaos. In particular, make a point of watching the voltage across the 32uF and 16uF capacitors and make a note of these voltages. You need to watch for a voltage that changes as you approach the 10-minute point.
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Old 18th Oct 2019, 11:08 pm   #20
Lef de art
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Default Re: Reel to reel valved tape recorder Geloso G258, problem

And yes the problem is in capacitors !!!
I must change the electrolytic and papper capacitors.
Any ideas where i can buy them on line

*16μf 200ν-250v
*32μf 350v-500v
*25μf 30v
*150MF 15v
*0,0047μf 20%
*0,0022μf 25%

And a double one 25+25μf 200vcc-350v ( i say it correctly? )


I feel that the project will have a happy end and I'm really excited
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