nut

valve problem?

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I have a jolida fx2 dac.

Just bought some raytheon 5575 valves off these forums and adaptors off ebay.

Used for first time today.

1)  Left channel    -   has bad hum increasing with volume.
     Right channel -   sounds good.

I swap over the valves (not the adapters).

2)  Left channel    -   sounds good.
     Right channel -   no sound at all from speaker.

I swap valves back and forth.
Each time i swap, it goes 1) 2) 1) 2).....etc (above)

There seems to be one good valve.

The other valve seems to have problems as when in one channel it hums, and when in the other channel it looses sound altogether.

I have repeated this 6 times.

Valve problem?

Or am i missing something?

Thank you.

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9 minutes ago, nut said:

I have a jolida fx2 dac.

Just bought some raytheon 5575 valves off these forums and adaptors off ebay.

Used for first time today.

1)  Left channel    -   has bad hum increasing with volume.
     Right channel -   sounds good.

I swap over the valves (not the adapters).

2)  Left channel    -   sounds good.
     Right channel -   no sound at all from speaker.

I swap valves back and forth.
Each time i swap, it goes 1) 2) 1) 2).....etc (above)

There seems to be one good valve.

The other valve seems to have problems as when in one channel it hums, and when in the other channel it looses sound altogether.

I have repeated this 6 times.

Valve problem?

Or am i missing something?

Thank you.

Cant you put the original valves back on? 

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The original valves work fine.

I had the problem last night.

Gave up and put the ecc83 back in and all ok.

I tried again today, exactly the same problem.

The weird thing of one valve good, and the other producing hum or nothing depending on which channel it was in.

Ecc83 back in now and sounding good.

It seems the adapters are the good valve works in both.

The bad valve has different results in each adapter.

Confused and weird.

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Moderator

First, it seems likely beyond much doubt that one valve is faulty. Don't keep using it. Depending on what the fault is, there is the potential to do some harm.

Second, sorry to sound like 'mother knows best', but do you have it from Jolida that the 5755 is a suitable substitute? The specs for 5755 and 12AX7 are certainly not identical, so I'm not in the least surprised they sound different.

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18 minutes ago, nut said:

The original valves work fine.

I had the problem last night.

Gave up and put the ecc83 back in and all ok.

I tried again today, exactly the same problem.

The weird thing of one valve good, and the other producing hum or nothing depending on which channel it was in.

Ecc83 back in now and sounding good.

It seems the adapters are the good valve works in both.

The bad valve has different results in each adapter.

Confused and weird.

I still have the original tung sol valves on my jolida dac..sound pretty good to me..i subscribe to the school of ' if it works? Why break it? ' lol 

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The  5755 seems to be quite widely used by the fx dac owners.

Yes, the dac sounds great with most valves.

Thanks or the replies.

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Without meaning it as criticism, 'quite widely used' is different from being considered suitable by the manufacturer.

People when they design circuits choose a particular valve for a particular reason. Quite often there is no problem in substituting others, but the sound will certainly be different. The operating points differ and it's highly likely that the valves aren't operating (if different) in their most linear range. Of course, this may be considered 'better' as it may increase even-order harmonic distortion or emphasise different parts of the frequency range slightly.

There are, however, plenty of cases where a designer allows one particular property of a valve to run relatively close to the operating limits. In these cases, a 'close' substitute might well be running beyond one or other limit. It's not common and most valves are surprisingly robust. However, it's not unknown. There are many aspects to valves other than the maximum plate voltages and operating currents, and some are usually overlooked.

My advice is the same as it always has been. Unless you have the specific say from the manufacturer or designer that a certain substitute is fine to use, you may be taking a risk. Without doubt, in most cases you can swap just about any double triode for any other and still get the thing to make a noise. Close substitutes are most times no problem. It's just that on rare occasions, they can be.

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I'll just chip in that yes, one 5755 valve definitely seems faulty and shouldn't be used - it should be replaced/refunded FOC. As to whether you should use it at all I have no idea,  I'll leave Richard to do the explaining.

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I got some NOS 6SN7, one was feeding back. If I put my gas around it, the hum gets a lot lesser. Dealer swapped for me. But the new one had a very mild hum. So swapped again and was ok. That’s the fun of valves or NOS valves.

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Yeah ... tap the chassis and you know ... but in a well designed component they sound so sweet.

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Microphony is a serious problem with a lot of NOS valves, because it's difficult to test for and no 'standard' test includes it. A lot of small signal valves are reasonably immune, but not all by a long stretch.

Generally, 12A*7 are pretty good, 6922s can be tricky and 5687s are often bad. I winder whether the actual construction has something to do with it, because octal base valves in general, not just 6SN7s and the like, seem particularly prone. Octal base pentodes are the worst of the lot. Most are little used and cheap, but it's just as well. Buy ten, throw eight away.

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But funny thing is the 6SN7s were used in WW2 field radios. They need to be physically durable. Nature of the valves perhaps ...

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Posted (edited)

Rigid construction and physical robustness are prime for military spec, but age takes its toll I suppose and rigid construction leads to more likelihood of microphony. Also, remember that a lot of military valves were designed for high frequency use, so microphony at audio frequencies was never an issue.

Old valves. When they're good, they're superb. It's just that they come with their own barrow load of issues...

Edited by rabski
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2 minutes ago, rabski said:

Rigid construction and physical robustness are prime for military spec, but age takes its toll I suppose and rigid construction leads to more likelihood of microphony. Also, remember that a lot of military valves were designed for high frequency use, so microphony at audio frequencies was never an issue.

Old valves. When they're good, they're superb. It's just that they come with their own barrow load of issues...

But we love them ... Darn 60-70 year old valves 😬

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