Tandberg 64x after changing capacitors

[ms660]

V6 pin 6 anode voltage is low but I wouldn't of thought it would cause lack of signal.

The last hum test you did in post#172 suggests a signal discontinuity between the grid of V6a and the grid of V6b, you could try swopping V5 and V6 over and see if the good channel goes bad, if no different then check carefully all the work you have done between the anode circuit of V6a and the grid of V6b, check for cracks in the printed circuit, dry joints and make sure the components you've replaced are of the correct value and that the valve pins and socket contacts are clean etc.

Lawrence.

[Levente]

Thanks Lawrence....

I have replaced the V5 tube holder...is the V5 completely ok? I have not replaced the V6 tube holder, its the old one. Should I only focus on V6? Just to exclude that I have not messed up the V5 while I replaced the tube holder last year...

Thank you....

[ms660]

I'll post up a drawing, hopefully within the hour.

Lawrence.

[ms660]

For anyone that might be following this thread:

Drawing for clarification of the last hum test and voltage measurements, heater voltages not shown but heater voltages were ok.

Lawrence.

[Levente]

Lawrence, thank you so much.

I have a good news. I had another look on the PCB next to the V6 tube. few months back I did a soldering with an extra rod. This extra rod was soldered to a place where touched another rod right next to it which should not be connected. This resulted a short i think. I have re soldered and BINGO. Both channels are working!

BUT ...I already know what will be my next headache. To equalize the two channels...they sounding sooo much different...one is with an extreme high treble the other one is low and both are lacking bass...

I have tried fiddling around all the head alignments, and with the osc. board, so far I can not have the same sound quality on the recording...

Again, thank you so much for your help! Really appreciate it...and I have learned a lot...

Levente

[ms660]

Well, some good news at last then, still need to get the playback sounding good.

Don't fiddle around anymore with the Osc board yet, the oscillator has no relevance to the playback function.

Can't remember what the playback head adjustments are without digging out the full manual, usually it's head height, zenith and azimuth, the adjustments are usually interactive, make sure there's no top or bottom tape curl when the tape is running through the tape guide.

The heads have to be clean/spotless can't emphasize that enough, if brown/orange stuff is on the cotton bud when cleaning then keep cleaning until there's non left.

Keep at it.

Lawrence.

[Levente]

Sorry, i made a mistake saying "playback"...its the recording and listening back on the spot on AB test...thats hy i thought it has something to do with the oscillator board.

I am reading the manual and actually there is loads of info about it, specially those funny looking resistors which can be adjusted...

ill clean the heads again, and will report back if any improvement.

Thanks Lawrence,

Levente

[ms660]

Remember you need to sort the playback out first including any playback head adjustments with that pre-recorded tape you recently got, record or record with monitoring can come later.

Lawrence.

[Levente]

Thanks Lawrence,

Re cleaned the heads and it seems that I have managed to equalize the playback head. Now the big job is tomorrow....the bias head and record head...i am going to follow the manual on this. It sounds a bit complicated.....

Levente

[Levente]

I cant get the recording head and the two channels eq'd equally. Its sooo difficult. Spent the whole day on this and difference between the two channels is significant.

One channel is very high on treble the other one is very low in treble, very muffled...have tried to equalize on the oscillator pcb., moving the bias head around, alignment etc....i can equalize the volume but not the sound....

what could be the issue? changing more components ?

[Levente]

Hey Guys, Lawrence..hope you are doing very well and hope you don't mind me appearing here again!

I can not get the sound right on the recording....playback is fine.

And i suspect something is not right on the oscillator board but this is only my guess....

Is it normal having AC voltages going in to the oscillator board on the Green wire 55.5 VAC and yellow wire 67.1 AC? I thought it should be DC there but maybe I am completely wrong here...

hat I have learned from you Lawrence bout the those 3 leg transistors and the emitters.....they should have some voltage of DC there.

I have re measured them again.

We have 4 of these 3 leg transistors.

2 of them measuring voltages in all 3 legs, and two of them measuring DC voltages only on the legs on the sides...

I guess again something is not right as all 4 should have at least the sme measurement if right next to each other on the same board...?

Please if you can advise on this I would much appreciate it! Thank you so much.

Levente

[ms660]

I think we've been through voltage checks on the bias board before, that said, check the voltage on both sides of C602 and C604, there should be a DC voltage on one side of those capacitors measured with respect to chassis, I would expect that voltage to be approx. 12 volts DC if the bias output transistors are ok.

Lawrence.

[Levente]

Hi Lawrence,

Thanks for your reply.

Yes, there are DC voltages on one side of both capacitors.

I thought the sound problem should be somewhere on the bias board as i can not get the bias right at all....it has a "lisping" sound when i record music and one channel is really distorted with really bad signal.

That's why I've suspected the transistors...as 2 out of the 4 in the row has no readings on the middle emitter legs while the others has DV voltages on all 3 legs...

Could be the Styroflex capacitors or the small Polisytren caps as these are connected to these transistors or the actual transistors are faulty?

Thank you

[ms660]

"Yes, there are DC voltages on one side of both capacitors."

Yes, but what are the voltages?

Lawrence.

[Levente]

There are 11.8 and 11.9 VDC.

Thanks, Levente

[ms660]

That suggests that the bias output transistors are ok.

You might be lucky sorting out the record problem or you might be not, if you've adjusted any of the preset components in the record circuit or the bias circuit then they should be returned to their original positions.

The other important factor is that if you've adjusted the record or bias head the record head must be aligned properly in respect to the playback head and the bias head must be aligned properly with respect to the record head, If not then performance will suffer.

Doing any electrical adjustments in the record or bias section requires the proper equipment as indicated in the manual in order to get the proper results.

As has been said before check any work you might have done in the record circuit, any obvious valve voltage differences between the two recording channels will need investigating.

Lawrence.

[Levente]

Thanks Lawrence.

I am a bit stuck on this. Any other components you would suggest to check or replace on the bias board?

The two VAC differences coming in to the bias board are the ones needs to be checked?

I've spent two full days on aligning the heads following the manual...i never got it right, i have tried everything or at least what I am capable to do I guess...the playback head is fins and sounds great actually...

only these record/bias I can not get through. I just dont ant to spend more hours fiddling on the alignment if the problem source is one or two other components on the bias board for example..

I am a bit lost....

Thanks for your input and help!

Levente

[ms660]

If the erase is working then the bias oscillator must be working, if that's the case then there's not a lot to go wrong component wise on the bias board that would cause the symptoms you have. eg both channels poor.

Voltage wise, all you can do in the record section is to check the valve voltages to see if any of them are out on one channel with respect to the other channel.

With the right equipment such as an audio signal generator and an oscilloscope the root of the problem would soon be found.

Lawrence.

[Levente]

Thanks Lawrence.

Will check again the soldering and all the components on the recording board...unfortunately such equipment's are far away from my knowledge how to use them.

If I was in the UK and you would offer a labour on this machine I would be gladly send you and of course pay for the work...

Levente

[ricard]

I don't know if this helps, but my experience has been that on the 64X the high frequency response on record isn't as clearly affected by the bias level as on machines with conventional bias. Traditionally, the high frequency response is the most critical parameter governed by the bias level, so everything else being OK, one uses the high frequency response to set the bias level correctly. But on the 64X the correlation is not at all as obvious. Which is strange because on another cross-field machine I have (Tandberg 9141X) adjusting the bias level has the same influence on high frequency response as I'd expect from any tape machine.