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Peter Wieck Peter Wieck is offline
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Default Chinese Rectifiers

Some years ago, I acquired a Scott LK150 amp - which came to me equipped with purportedly NEW Chinese 5AR4s. I did not even test the amp with those tubes in place - they were immediately replaced with a pair of GEs from my stock. Meanwhile, the Chinese tubes have been sitting in my junk-box for the last eight (8) years.

Yesterday, I had a bit of time, and the big Hickok was out for other reasons, so I decided I would test the tubes.

The first one immediately smoked its filament. The second one, after about 20 minutes, melted into a mess - almost cartoon-like. Everything inside the glass is tilted or rippled. The second one tested marginal before the melt, by the way.

Had they been in the Scott (or any amp), the consequences could have been nasty.

Friends don't let friends use Chinese Tubes.


Peter Wieck
Melrose Park, PA
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Big Bad Bob Big Bad Bob is offline
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On 11/02/15 03:39, Peter Wieck so wittily quipped:
The first one immediately smoked its filament. The second one, after about 20 minutes, melted into a mess - almost cartoon-like. Everything inside the glass is tilted or rippled. The second one tested marginal before the melt, by the way.


Friends don't let friends use Chinese Tubes.


some are good, some are not, apparently. I've heard that Ruby buys
(some of) their tubes from China, then tests them before selling as
'Ruby'. But that might be a rumor.

need reputable sources, for sure.

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Peter Wieck Peter Wieck is offline
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On Monday, November 9, 2015 at 1:17:20 PM UTC-5, Big Bad Bob wrote:
On 11/02/15 03:39, Peter Wieck so wittily quipped:
The first one immediately smoked its filament. The second one, after about 20 minutes, melted into a mess - almost cartoon-like. Everything inside the glass is tilted or rippled. The second one tested marginal before the melt, by the way.


Friends don't let friends use Chinese Tubes.


some are good, some are not, apparently. I've heard that Ruby buys
(some of) their tubes from China, then tests them before selling as
'Ruby'. But that might be a rumor.
need reputable sources, for sure.


Bob:

Here is the issue. I remember testing these tubes when they arrived (the amp was well used), and they did rectify. Meaning, any local test will be 'good' until it is not. Of course, this may be written about any tube, irrespective of brand - but Chinese tubes fall into their own category. Most reputable 5AR4 tubes fail fairly gently - not spectacularly.

BUT, over an 8-year period, one apparently got gassy enough to pop the filament, the other slagged. This was 8 years of NO USE.... not 8 years and hundreds of hours - which would be understandable.

The going rate on a functional LK150 is up to/around $1,200 these days. I would not risk such a device to someone else's tests. I am sure that Ruby would replace a slagged tube, but would they replace a slagged power transformer? Somehow, I do not think so. And, yes, I do fuse the primary. I only hope the fuse is fast enough to save things under dire conditions.

And, one of the reasons I am hesitant about re-branded tubes anyway unless I am dead-sure of the provenance.

Peter Wieck
Melrose Park, PA

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Big Bad Bob Big Bad Bob is offline
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On 11/09/15 11:46, Peter Wieck so wittily quipped:
The going rate on a functional LK150 is up to/around $1,200 these days. I would not risk such a device to someone else's tests. I am sure that Ruby would replace a slagged tube, but would they replace a slagged power transformer? Somehow, I do not think so. And, yes, I do fuse the primary. I only hope the fuse is fast enough to save things under dire conditions.

And, one of the reasons I am hesitant about re-branded tubes anyway unless I am dead-sure of the provenance.



I here ya - don't want the 50 cent fuse protected by the $250 transformer

are these tubes mounted vertically or horizontally? I've seen 5V
rectifiers mounted horizontally before, in an old hifi from the 50's.
That might affect how long the tubes live, depending on whether they're
designed to take it or not.

most guitar amplifiers have them vertically, but upside down. Just
thinking if maybe the tubes were intended to be vertical pointing up,
and then the amp design has them "some other way", and they got cheap
with the supporting framework around the filament. Then it starts to
sag internally, shorts against the plate, *poof*


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On Friday, November 13, 2015 at 2:36:18 AM UTC-5, Big Bad Bob wrote:



are these tubes mounted vertically or horizontally? I've seen 5V
rectifiers mounted horizontally before, in an old hifi from the 50's.
That might affect how long the tubes live, depending on whether they're
designed to take it or not.


They are mounted conventionally (base-down).

Quite a bit of eequipment mounts tubes horizontally, a very few upside down.. Hickok mounts its tester tubes horizontally - specifically against handbook instructions for the 83 as it happens. Zenith and Motorola have a line of radios with the chassis mounted 'upside down' and Lafayette (amongst a few others) has a line of audio components with the tubes mounted horizontally.

I keep a big Hickok tester, but I have replaced the rectifiers with SS equivalents to remove the issue. The whole process takes about an hour (and a few bucks for the tube bases, resistors and diodes) most of which is the recalbration process.

But cutting to the chase - Chinese tubes carry a risk that, as measured against the value of the equipment, seems unreasonable to me. Screening and testing gives only momentary results. The long-term behavior is of much greater interest to me, and observed failure modes if available. As I work mostly in vintage equipment reaching back to the '20s, I have had more than the usual few opportunities to observe failure modes. And those observations have served me well.

Peter Wieck
Melrose Park, PA
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