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adchesney adchesney is offline
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Default 300B dead after 9 months - HELP

Dear Folks,

This is my first post (so go easy!) - I purchased a 300B amp off EBay and I have really enjoyed it. Previously I built an Edison 30 amp.

However, the 300B has died, my daughter said the "middle bulb went pop". This "bulb" she is referring to is the 274B tube.

My question is...how long should these valves last? And what could cause premature failure.

The amp is the same as this: http://cgi.ebay.co.uk/King-300B-Clas...QQcmdZViewItem

Regards

Andrew (Yateley, UK)
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maxhifi maxhifi is offline
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Default 300B dead after 9 months - HELP

Tubes should last a while, but failures do happen. Best would be to test the
274B, then buy a NOS 5R4G, and replace the 274B with it.




"adchesney" wrote in message
...

Dear Folks,

This is my first post (so go easy!) - I purchased a 300B amp off EBay
and I have really enjoyed it. Previously I built an Edison 30 amp.

However, the 300B has died, my daughter said the "middle bulb went
pop". This "bulb" she is referring to is the 274B tube.

My question is...how long should these valves last? And what could
cause premature failure.

The amp is the same as this: http://tinyurl.com/2dcg2p

Regards

Andrew (Yateley, UK)




--
adchesney



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Eeyore Eeyore is offline
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Default 300B dead after 9 months - HELP



adchesney wrote:

Dear Folks,

This is my first post (so go easy!) - I purchased a 300B amp off EBay
and I have really enjoyed it. Previously I built an Edison 30 amp.

However, the 300B has died, my daughter said the "middle bulb went
pop". This "bulb" she is referring to is the 274B tube.

My question is...how long should these valves last? And what could
cause premature failure.


Any tube can go POP at any time.

It's part of the price you pay for your perversion.

Graham

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Phil Allison Phil Allison is offline
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Default 300B dead after 9 months - HELP


"adchesney"

This is my first post (so go easy!) - I purchased a 300B amp off EBay
and I have really enjoyed it. Previously I built an Edison 30 amp.

However, the 300B has died, my daughter said the "middle bulb went
pop". This "bulb" she is referring to is the 274B tube.



** Went pop = the glass has broken ?????


My question is...how long should these valves last?



** How long is a piece of string .....


And what could cause premature failure.



** Tell us what failed.

The glass, the heater/cathode or has it arced internally ?

Tried a new valve yet - know if there is another failed part ?




......... Phil


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West West is offline
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Default 300B dead after 9 months - HELP


"adchesney" wrote in message
...

Dear Folks,

This is my first post (so go easy!) - I purchased a 300B amp off EBay
and I have really enjoyed it. Previously I built an Edison 30 amp.

However, the 300B has died, my daughter said the "middle bulb went
pop". This "bulb" she is referring to is the 274B tube.

My question is...how long should these valves last? And what could
cause premature failure.

The amp is the same as this: http://tinyurl.com/2dcg2p

Regards

Andrew (Yateley, UK)


Hi Andrew,

With limited info, I would take a SWAG to say that there is a 50% chance
that a component failure cause your valve to get dorked. Check for this
before replacing the valve (preferably with a 5R4G).

Cordially,
west




--
adchesney





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jaap[_3_] jaap[_3_] is offline
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Default 300B dead after 9 months - HELP

François Yves Le Gal wrote:
....
I'm pretty sure that the Chinese 274B has arced because of the combination
of too little R on the B+ windoings (vintage valves call for at least 100R
series R) combined with too much capacitance in the first filtering
stage4µF is recommended, 8µF is max).

....

So, indeed, the expected life span of a Chinese rectifier in again a
Chinese design might justify for an prologued insurance. More so since
this amp is equipped with a regulated PSU: four '2A3' triodes @50mA
each, 10% headroom for the regulator gives 220mA and that's quite a lot
for vacuum. WTH is a Lose True Degree 8[]
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Default 300B dead after 9 months - HELP

jaap wrote:
More so since
this amp is equipped with a regulated PSU: four '2A3' triodes @50mA
each, 10% headroom for the regulator gives 220mA and that's quite a lot
for vacuum.

Yours has two 300B's but the story is the same: there's quite some
strain on the rectifier tube, it might be calculated on the edge as
voltage at the output tranny will be over 400V... Without the schematic
it is guessing but probably it would have been wiser to use sand for
rectification.
I would recommend against swapping rectifier tubes if you do not know
what voltage drop to expect. Contact the seller for assistance or buy
another (few) 274 tubes as they come cheap
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maxhifi maxhifi is offline
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Default 300B dead after 9 months - HELP


"jaap" wrote in message
l.nl...
jaap wrote:
More so since
this amp is equipped with a regulated PSU: four '2A3' triodes @50mA each,
10% headroom for the regulator gives 220mA and that's quite a lot for
vacuum.

Yours has two 300B's but the story is the same: there's quite some strain
on the rectifier tube, it might be calculated on the edge as voltage at
the output tranny will be over 400V... Without the schematic it is
guessing but probably it would have been wiser to use sand for
rectification.
I would recommend against swapping rectifier tubes if you do not know what
voltage drop to expect. Contact the seller for assistance or buy another
(few) 274 tubes as they come cheap


I have a pair of RCA MI-12188A amplifiers which each use a Sylvania 5R4GYB.
The power supply consists of a 750-0-750 transformer, into a large choke -
and the current draw of the output stage is on the order of 200mA at 600V.
Six years of problem free daily operation, and I got the tubes used with the
amplifiers! Their emmission has not dropped noticibly on the TV-7, either.

Don't bother with Chinese tubes, if you want reliability, find some NOS
Sylvania. In my limited experience, the best tubes (from a reliability
perspective) are

Sylvania
GE
RCA

in that order.


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jaap[_3_] jaap[_3_] is offline
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Default 300B dead after 9 months - HELP

maxhifi schreef:
"jaap" wrote in message
l.nl...
jaap wrote:
More so since
this amp is equipped with a regulated PSU: four '2A3' triodes @50mA each,
10% headroom for the regulator gives 220mA and that's quite a lot for
vacuum.

Yours has two 300B's but the story is the same: there's quite some strain
on the rectifier tube, it might be calculated on the edge as voltage at
the output tranny will be over 400V... Without the schematic it is
guessing but probably it would have been wiser to use sand for
rectification.
I would recommend against swapping rectifier tubes if you do not know what
voltage drop to expect. Contact the seller for assistance or buy another
(few) 274 tubes as they come cheap


I have a pair of RCA MI-12188A amplifiers which each use a Sylvania 5R4GYB.
The power supply consists of a 750-0-750 transformer, into a large choke -
and the current draw of the output stage is on the order of 200mA at 600V.
Six years of problem free daily operation, and I got the tubes used with the
amplifiers! Their emmission has not dropped noticibly on the TV-7, either.

Don't bother with Chinese tubes, if you want reliability, find some NOS
Sylvania. In my limited experience, the best tubes (from a reliability
perspective) are

Sylvania
GE
RCA

in that order.


I don't know if your mono blocks are comparable but they probably lack
the active PSU. Agree that nothing (sonic wise) beats thermo
rectification and that in a good design tubes live long.
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Default 300B dead after 9 months - HELP

François Yves Le Gal wrote:
On Mon, 06 Aug 2007 18:37:45 +0200, jaap wrote:

Yours has two 300B's but the story is the same: there's quite some
strain on the rectifier tube


The 274 is spec'ed at 160 mA max into 4 µF for C1 (RC Pi filter) and
shouldn't deliver more than 120 mA into 8 µF. Anything above 8 µF (or above
say, 30 µF to tal capacitance in a CLC combination) spells disaster.

Two 300B in SE class A plus two 6SN7 and two 12AT7 come very close to the
max.

I would recommend against swapping rectifier tubes if you do not know
what voltage drop to expect.


Hmmm. You can safely replace a 274 with a 5U4GB, provided that the xformer
can supply 3 A for heating (vs. 2.4 A for a 274). NOS valves from Tung-Sol
or Sylvania (my two faves, but the RCA et al. are also well worth
considering) are quite cheap and very easy to find.

Contact the seller for assistance


The seller describes the amp a using a "Hi-End Super Regulator Power
Supply".

Have a look at a picture of the amp:
http://hi-end.on9mart.com/products/a...8-photo_13.JPG

Where is the "Regulator" ? All i see is a basic CLC PS.

I'm not sure that the seller can be of any help here...
:-)



Outch

A voltage regulator is designed to work within certain limits, that's
why I advised keeping the exact voltage. But if there isn't any, go ahead.


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Peter Wieck Peter Wieck is offline
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Default 300B dead after 9 months - HELP

On Aug 3, 6:43 pm, "West" wrote:

With limited info, I would take a SWAG to say that there is a 50% chance
that a component failure cause your valve to get dorked. Check for this
before replacing the valve (preferably with a 5R4G).


That is highly unlikely with Chinese tubes. What is far more likely is
that this (and equally likely the rest of the tubes in the unit) are
marginal at-best and that the OP is exceedlingly lucky that little
damage was done other than the rectifier tube failing.

From the "looks" of the amp, it is pretty clear that most of the tubes

were chosen for their looks vs. for any other particular reason with
specific reference to the 274B and its nice fat ST shape. That and the
"300B" cachet. Were I to let the cynic in me escape, I would posit
that a couple of hack designers got together and asked each other what
was on the cutting edge of popularity these days.... and came up with
the 300B, the 6SN7 and so forth. Then the fancy aluminum trim....

Ah, well.

Peter Wieck
Wyncote, PA

p.s. Perhaps on the FAQ, one of the general items that should be
included would be a general warning on "Things Chinese" and the
problems that come along with them.

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