300B failed again

[45]

Originally Posted by FullRangeMan

Manta bought from a large Germany shop, surely a respected vendor and had this bad tubes!!

I start suspecting noone test any tube, by lack of time, test equip and qualified personal.
Too bad, so rest us to buy at VTS, UPSCALE and others top money tube brokers...

That's the bad thing about buyng on-line. If you can go to a shop you can ask for a test. That's the way I do usually for expensive stuff. If I cannot I just don't buy it. There are options as good as, or even better than, the expensive 300B. I think some people just cannot cope with this statement......they must have a 300B, regardless of anything, otherwise it's not good enough!

[the_manta]

Ok, thanks everybody.
I will go for the GuiGuang 300B. The Shuguang 300B-98 are nearly the same price but I give the GuiGuangs a try.
With JJ I had similar problems as with EH now. Their preamp tubes and rectifiers are very fine but not their power tubes. I've had it with their EL34...

The EH now goes in my display cabinet and my dog got the box it came in. He ripped it apart in seconds. Take that New Sensor corp !

[cotdt]

I like your dog!

[FullRangeMan]

Originally Posted by the_manta

Ok, thanks everybody.
I will go for the GuiGuang 300B. The Shuguang 300B-98 are nearly the same price but I give the GuiGuangs a try.
With JJ I had similar problems as with EH now. Their preamp tubes and rectifiers are very fine but not their power tubes. I've had it with their EL34...

The EH now goes in my display cabinet and my dog got the box it came in. He ripped it apart in seconds. Take that New Sensor corp !

Hi,
Any opinion on sound quality on these Guiguang 300B??

I also bought a pair for stock, they are metal plate and black base, no date code.

[hrnoevil]

I have exactly the same problem as the_Manta experienced. I found one of my EH 300B gold grid tube with only half of the heater lit up. There is not a big difference in sound quality at low level but will distort when the volume is turned up. This pair was about 6 years old and cost US$139.95 a pair at the time. I have tried the Chinese Shuguang 300B before but didn't like it. So I have ordered a new matched pair of the same thing which now cost US$190.00 a pair plus shipping. I am not sure if this is a common problem with the EH 300B.
One time I pulled out my amp from underneath the rack to take a picture while it is hot and running, I wonder if this contributed to the breaking of one side of the filament.
I wonder is there anything I can do to get these tubes live longer, like putting a small resistor in series to reduced the voltage to, say, about 4.8 v. or something. Anybody tried the new Psvane 300B ? Apparently it is made in China by a joint venture of foreign investors and ex-Shuguang Engineers. The purpose is to clone the infamous WE 300B using the same technique and material.

[kevinkr]

Originally Posted by hrnoevil

<snip>
One time I pulled out my amp from underneath the rack to take a picture while it is hot and running, I wonder if this contributed to the breaking of one side of the filament.
I wonder is there anything I can do to get these tubes live longer, like putting a small resistor in series to reduced the voltage to, say, about 4.8 v. or something.<snip>

It is quite possible that disturbing the amplifier with the tubes hot may have contributed to this problem.

I've had this problem (half filament dead) with a couple cheap Valve Arts 300B, and a number of SV300B - both more than a decade ago.

I've found CCS based heating of dhts to be generally a good idea, since inrush current is limited by the CCS to that required for normal operation you have neither the thermal nor magnetic stress encountered during uncontrolled inrush. I can recommend Rod Coleman's CCS having used them to heat GM70 for about 15 months now.

[Rod Coleman]

Thanks Kevin!

This failure does seem to have been a big problem with Svetlanas, Sovtek/EH and many other modern DHTs.

Using them with ac-heating, especially where the transformer is able to supply many amperes at start-up, is likely to be the biggest risk. When the filament winding is on the same transformer core as the HT(B+) supply, a high starting filament current is certain, because the HV secondary is effectively unloaded at switch-ON. The filament winding will give higher than normal voltage, and the cold-filament resistance of the 300B is less than 1 ohm (instead of 4 ohm hot). In this case, starting-current of over 5A is likely.

[Rod Coleman]

I hope DIYers are not scared away from the EH 300B gold grid though - the newest version of these is very well constructed and aligned, and it sounds far better than previous versions.

[FullRangeMan]

Originally Posted by hrnoevil

I have exactly the same problem as the_Manta experienced. I found one of my EH 300B gold grid tube with only half of the heater lit up. There is not a big difference in sound quality at low level but will distort when the volume is turned up. This pair was about 6 years old and cost US$139.95 a pair at the time. I have tried the Chinese Shuguang 300B before but didn't like it. So I have ordered a new matched pair of the same thing which now cost US$190.00 a pair plus shipping. I am not sure if this is a common problem with the EH 300B.
One time I pulled out my amp from underneath the rack to take a picture while it is hot and running, I wonder if this contributed to the breaking of one side of the filament.
I wonder is there anything I can do to get these tubes live longer, like putting a small resistor in series to reduced the voltage to, say, about 4.8 v. or something. Anybody tried the new Psvane 300B ? Apparently it is made in China by a joint venture of foreign investors and ex-Shuguang Engineers. The purpose is to clone the infamous WE 300B using the same technique and material.

Wow this golden paper boxes are very beautiful.
They think the tube not need to perform good with this fancy package...
6 years its too much time, seems a fragile cathode or solder so far in this thread.

[kevinkr]

Originally Posted by FullRangeMan

<snip>
6 years its too much time, seems a fragile cathode or solder so far in this thread.

Inrush current is a source of many filamentary problems with these dhts, while a CCS will not eliminate failures due to defects it may markedly reduce filament breakage and stretching/sagging due to inrush related stress.