Polymer guy here. 
I first became aware of this when salvaging caps out of telephone equipment that had been used outdoors. The polyester caps were in various states of degradation, but the mica caps were fine (polypropylene was rare in those days). The caps worked poorly, and measurements confirmed why. I disassembled a few, ran IR spectra, and clearly saw degradation in the dielectric.
I first became aware of this when salvaging caps out of telephone equipment that had been used outdoors. The polyester caps were in various states of degradation, but the mica caps were fine (polypropylene was rare in those days). The caps worked poorly, and measurements confirmed why. I disassembled a few, ran IR spectra, and clearly saw degradation in the dielectric.
It's far better than paper- paper is absolutely horrible, even with oil impregnation. And in normal domestic use, the lifetime of polyester caps should be excellent. But put them in an environment with 60° temperature and 100% humidity swings and it will take a remarkable encapsulant to keep them reliable.
Yes I was thinking of that, too. I don't have lots of money to spend unfortunately.
Their are currently Sovteks in there, so as long as the amps sound fine I think I'll leave it that way.
Soon I'll get another tube hybrid amp which has larger tubes don't know yet exactly which model but I'll find out. The amp is a little older than these so might need to replace the tubes earlier.
Their are currently Sovteks in there, so as long as the amps sound fine I think I'll leave it that way.
Soon I'll get another tube hybrid amp which has larger tubes don't know yet exactly which model but I'll find out. The amp is a little older than these so might need to replace the tubes earlier.
Don't take any notice of what is printed on the outside of the glass, although the etch code is less likely to mislead. If you really want Mullard innards at a slightly more reasonable price, then look for other Philips brands (e.g. (British) Tungsram, Valvo, Philips). Many of these were made in Blackburn. Even some cheap rebranders would sometimes sell off surplus Mullards.
That's very cheap. They usually sell for much, much higher.
I'll have a read here, might be interesting:
Preamp Tubes Review
I'll have a read here, might be interesting:
Preamp Tubes Review
Bear in mind that many reviews are based on guitar amps, so only limited read-across to audio. Also only a small number of samples of each type (sometimes 1!) are often used, and only a small number of amps. Finally, some of the issues raised relate to that valve in that amp biassed in that way and seeing those impedances - put that same valve in your amp and it could sound different.
Some guitar amps have quite high values of grid stopper resistors. This means that the HF rolloff can be quite low and set principally by valve internal capacitances multiplied by the Miller effect. In effect, they are using valve swapping (tube rolling) as a tone control but usually without realising this. This is not an issue to anything like the same extent in audio.
Some guitar amps have quite high values of grid stopper resistors. This means that the HF rolloff can be quite low and set principally by valve internal capacitances multiplied by the Miller effect. In effect, they are using valve swapping (tube rolling) as a tone control but usually without realising this. This is not an issue to anything like the same extent in audio.
most of the times it´s a matter of patient
ecc82 | eBay
5x Mullard ECC82 (vintage 60's 70's tube/valve) | eBay
ecc82 | eBay
5x Mullard ECC82 (vintage 60's 70's tube/valve) | eBay
used , they still do may hours in good condition , i tryed some new Ei Tubes they dont sound better than the used mullards.
see this treat ask the OP he might have some ecc82/12ax7 new old stock
http://www.diyaudio.com/forums/tubes-valves/212040-found-tons-tubes-many-other-parts.html
see this treat ask the OP he might have some ecc82/12ax7 new old stock
http://www.diyaudio.com/forums/tubes-valves/212040-found-tons-tubes-many-other-parts.html
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scope
Alright guys,
I had to take the smaller 7100 out of my car as the slight distortion had become huge.
Together with my father we had a good look at the two tube hybrid amps. The smaller 7100 is clearly distorted when listening to it, and the scope shows it clearly as well.
Please have a look at these pics:
ImageShack® - Online Photo and Video Hosting
ImageShack® - Online Photo and Video Hosting
ImageShack® - Online Photo and Video Hosting
ImageShack® - Online Photo and Video Hosting
ImageShack® - Online Photo and Video Hosting
The scope pictures were taken with 4 ohm speakers and RCA connected with no music playing. Removing the RCA's did not have any effect. The scope's probes were on the speaker output terminals, where the speaker wires were connected.
These were the scope settings for pics 7100 left and right:
Amplitude: 0.2V / Division
Time / Division : 5 microseconds
The signal the scope is showing is some very high frequency noise / inferference.
The time between each peak is 18 microseconds. the amplitude from peak to dip for the right channel is approx. 800 millivolts which is a lot which explains the badly distorted sound on the smaller 7100.
The left channel has 250 millivolts amplitude.
I can't tell which pic is which for the 7150, as we changed the amplitude settings and forgot to write down which setting we had for which channel.
Anyway, the right channel has an amplitude of approx 220 millivolts from peak to dip, the left channel approx 100 millivolt.
This amplifier does not have clearly audible distortion but I would really love to get the noise / interference down on this one as well.
What is this interference ? Is it the power supply ? We once measured a certain pin of a SG3524 on another amp with the scope and saw a similar signal if I remember correctly.
Please have a look at the board picture. Pressing down with the finger on R13 (right next to the coil) had an effect on the amplitude of the signal, it did not alter the signal itself.
Swapping the tubes left and right on the 7100 did not have any effect. We therefore did not try swapping the tubes of the 7100 with those of the 7150 as we believe the problem is not caused by the tubes.
Best regards,
Fred
Alright guys,
I had to take the smaller 7100 out of my car as the slight distortion had become huge.
Together with my father we had a good look at the two tube hybrid amps. The smaller 7100 is clearly distorted when listening to it, and the scope shows it clearly as well.
Please have a look at these pics:
ImageShack® - Online Photo and Video Hosting
ImageShack® - Online Photo and Video Hosting
ImageShack® - Online Photo and Video Hosting
ImageShack® - Online Photo and Video Hosting
ImageShack® - Online Photo and Video Hosting
The scope pictures were taken with 4 ohm speakers and RCA connected with no music playing. Removing the RCA's did not have any effect. The scope's probes were on the speaker output terminals, where the speaker wires were connected.
These were the scope settings for pics 7100 left and right:
Amplitude: 0.2V / Division
Time / Division : 5 microseconds
The signal the scope is showing is some very high frequency noise / inferference.
The time between each peak is 18 microseconds. the amplitude from peak to dip for the right channel is approx. 800 millivolts which is a lot which explains the badly distorted sound on the smaller 7100.
The left channel has 250 millivolts amplitude.
I can't tell which pic is which for the 7150, as we changed the amplitude settings and forgot to write down which setting we had for which channel.
Anyway, the right channel has an amplitude of approx 220 millivolts from peak to dip, the left channel approx 100 millivolt.
This amplifier does not have clearly audible distortion but I would really love to get the noise / interference down on this one as well.
What is this interference ? Is it the power supply ? We once measured a certain pin of a SG3524 on another amp with the scope and saw a similar signal if I remember correctly.
Please have a look at the board picture. Pressing down with the finger on R13 (right next to the coil) had an effect on the amplitude of the signal, it did not alter the signal itself.
Swapping the tubes left and right on the 7100 did not have any effect. We therefore did not try swapping the tubes of the 7100 with those of the 7150 as we believe the problem is not caused by the tubes.
Best regards,
Fred
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