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Old 11-08-2019, 03:26 AM   #21
Lef de art
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Default Re: Reel to reel tube recorder Geloso G258, problem

Yes i have cleaned it.
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Old 11-08-2019, 10:34 AM   #22
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Default Re: Reel to reel tube recorder Geloso G258, problem

Did you check/adjust recording bias?
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Old 11-08-2019, 11:07 AM   #23
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Default Re: Reel to reel tube recorder Geloso G258, problem

Yes i have checked it . Is not from bias, because the new records don't have bass. The playback process with the old records is ok.
I believe that the problem is in some capacitors close to mic input. I must rechange them. Perhaps one of them or more don't work correctly.
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Old 11-08-2019, 11:27 AM   #24
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Default Re: Reel to reel tube recorder Geloso G258, problem

Quote:
Originally Posted by Lef de art View Post
Yes i have checked it . Is not from bias, because the new records don't have bass. The playback process with the old records is ok.
I believe that the problem is in some capacitors close to mic input. I must rechange them. Perhaps one of them or more don't work correctly.
OK, I am confused: you said "The difference is on recording high frequencies .
The recording has lost high frequencies."

Are you losing high or low frequency?
How did you go about checking the recording bias?
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Old 11-08-2019, 03:09 PM   #25
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Default Re: Reel to reel tube recorder Geloso G258, problem

I think i have confused you with my bad English
I have lost bass from my new recordings after capacitor change.

The bias head it is cleared . Yes in playback mode works perfectly.
Only in the recording mode , records with lower bass.
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Old 11-10-2019, 02:16 PM   #26
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Default Re: Reel to reel tube recorder Geloso G258, problem

I would check the capacitors again, to make sure the values are good and soldering is done right.

What part did you use for "0.5 150V" ? Did you change the four "Commutatore" capacitors (for EQ on each tape speed) ?

I looked and there is a record bias oscillator, with 0.25MEG red trimpot. You might have to adjust it.
The Geloso G268 is almost the same circuit, if you can find the service manual on how to adjust the control.
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Old 11-10-2019, 04:36 PM   #27
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Default Re: Reel to reel tube recorder Geloso G258, problem

The 0.5uf/150v capacitor was replaced with 0.56/250v.

I haven't change the 4 commutator capacitors because are polystyrene capacitor and i know they don't really get bad through time. So this 4 capacitors are the same with the before (good low frequencys) and the after (bad low frequencys) situation.

The red trimpot is for changing the magic eye (EM84 valve) sensitivity . Does not effect the low frequencys or the sound generally.

Just to mention that the amplifier works nicely.
The problem with low frequencys is only in the new recordings.
So it must be a capacitor who is involved only in recording process. perhaps close to microphone input.
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Old 11-12-2019, 11:39 AM   #28
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Default Re: Reel to reel tube recorder Geloso G258, problem

Trying to configure what can be happen, and to exclude the possibility to have read wrong any capacitor inscription i decide to compare the removed capacitors with the inscription in schematic.
Comparing them i have found 3 big difference.

In the schematic in the chassis
2K/600v 0.02uf/150V
2K/400V 0.05uf/350V
5K/400V 0.005uf/50V

The inscription on them is very clear. You can see in the pictures.

Change them with the schematic values maybe will bring me more bass in recording mode ?

All the other removed capacitors correspod with the schematic.
I really can't configure what i made wrong.
I haven't mess them, i have changed them carefully one by one and everything is in correct position.
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Old 11-12-2019, 12:55 PM   #29
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Default Re: Reel to reel tube recorder Geloso G258, problem

I would say you have them mixed up. The voltages are also wrong. Check all pictures you have.

The 0.02uF and 0.05uF are switched with 0.002uF and 0.005uF.
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Old 11-12-2019, 01:56 PM   #30
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Default Re: Reel to reel tube recorder Geloso G258, problem

No i haven't.
The voltage in the schematic is different with the voltages in the chassis.
In the schematic the capacitor appear as 50k/250v and in reality was 50k/350v.

I have changed 11 papper capacitors.

The 8 capacitors are ok and the schematic values are very close with the chassis values.

But in the 3 i have mentioned the chassis value does not even close with the schematic value. That way was . I have changed them by the chassis values not by the schematic values.
For sure i haven't mixed up them. I mean are only 11 capacitors...

Sorry if i confused you more.

From schematic, can someone tell me witch capacitors are part of recording process ?
Maybe im was unlucky and one of them is defective

(Hope you understand my English. I don't know how the project will finish but for sure my English will level up at the end


And here is one video to see a good moment with very good sound from my first recordings. Now the bass is much more lower.

https://www.dropbox.com/s/wxrc30l9fd...10501.mp4?dl=0
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Old 11-12-2019, 11:44 PM   #31
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Default Re: Reel to reel tube recorder Geloso G258, problem

Don't worry your english is good

I would say the schematic has errors. Usually, you lose bass when a coupling capacitor is low in value. But here, some factory capacitors are 10X higher in value than the schematic.

OK, I would say the 2K/400V at the ("uscita" headphone?) jack should be bigger. This would only affect bass from headphones (or whatever uscita means), not recordings. It was 0.05uF/350V you found there?
Notice that the jack shorts the capacitor out when speakers are connected, so there would be no effect.

The other 2K/600V (to plate pin 5 EL95) is for the record bias oscillator. I'm not sure it is still working, there is a 0.25MEG red trimpot to adjust the oscillator and the big square on schematic is a test-point. It might best explain why recordings have no bass and sound tinny - no bias oscillator.
But the cap needs to be 600V and you removed a 150V part? This is why I don't believe you The only 0.02uF/150V cap is at the 12AX7 V1a grid.

The third different capacitor 5K/400V=0.005uF/?50V the value is good because 5K = 5,000pF = 5nF = 0.005uF
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Old 11-13-2019, 01:55 AM   #32
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Default Re: Reel to reel tube recorder Geloso G258, problem

Good morning guys.
The uscita headphones is for external speaker.
The red trimpot is for adjusting the sensitivity of EM84. Does not effect the recording or playback mode.


It is somehow strange the schematic to has errors because in the next model G268 how appeared two years later the schematic has the same values.

Im was thinking to change them again with new ones.
What you believe, to use the schematic capacitors or the factory capacitors?

The so big difference in the 5k capacitor from 500v to 50v dose not affect nothing?
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