Elochen EL34 tube amp tube

[beansprout]

I have an inexpensive tube amplifier that has 5U4G tube, rectifier tube (I think) that sometimes has little lightning bolts on power-up. Once, it made a flash that was bright enough to light up my living room. From what i've read here, this may be impurities in the tube. My question: Should I be thinking about ordering a new tube, or is this normal? The amplifier sounds quite nice to me so sound does not seem affected. The amp and tubes are only about 3 months old.
Thanks!

 

[gadget73]

Once those flash, they're usually toast. They also mostly do this when there is some other problem. Too big of a capacitor that abused it, a bad capacitor that is causing excess current draw, or just a bad tube. A good 5u4 in a reasonably sane circuit will not flash. I would replace that immediately and not use the amp again until I did.

Might try for some old US production ones. Those tubes are available by the box load for not much money.

 

[larryderouin]

+1 with Gadget. Use a DOMESTIC old stock 5u4gb, suggest RCA or GE. $12.00 @ abcvacuumtubes.com. No affiliation. I get 90% of my tubes from them except for Power tubes.

 

[FlaCharlie]

I have an inexpensive tube amplifier that has 5U4G tube, rectifier tube (I think) that sometimes has little lightning bolts on power-up. Once, it made a flash that was bright enough to light up my living room. From what i've read here, this may be impurities in the tube. My question: Should I be thinking about ordering a new tube, or is this normal? The amplifier sounds quite nice to me so sound does not seem affected. The amp and tubes are only about 3 months old.
Thanks!

This seems to be a common issue with the Chinese amps. Part of the problem is that the stock tubes are of questionable quality. But the other issue is that the value of the first capacitor after the rectifier tube is often way too large. The "designers" of these amps apparently don't know enough to read a tube data sheet, which specifies the maximum cap size for the various rectifier tubes.

https://tubedata.altanatubes.com.br/sheets/093/5/5U4GB.pdf

Part of the solution involves using quality tubes - old stock (new or strong testing used) American 5U4GBs. But before you replace the tube you need to open up the amp and check the value of that first cap. If the cap is too large you may still have problems after you install a better quality tube.

The data sheet lists the maximum at 40uf. Modern caps with the closest standard values are rated at 33uf and 47uf. In most all cases the 47uf will work fine. That's because tolerances on modern caps are much better and because most amps - especially the common SE Chinese ones - operate with a lower current draw than the tube (assuming a quality American tube) is capable of. Make sure the voltage rating of any new replacement cap is either the same or higher than the stock cap. Typically that will be a 47uf 450v cap.

 

[s-petersen]

LaoChen?

 

[avguytx]

LaoChen maybe?

 

[beansprout]

Thanks for all the great advice! And, yes, Laochen...pardon my typo.

 

[beansprout]

Hey FlaCharlie, I opened up the bottom of my amp and it appears there is a 100uF capacitor that is in line with the rectifier tube. So on your recommendation, I'd like to get a 47uF, 450 volt to replace it.
If I order one through Madison, what exactly do I specify other than 47 uf 450 vac?
Thanks!

 

[FlaCharlie]

Hey FlaCharlie, I opened up the bottom of my amp and it appears there is a 100uF capacitor that is in line with the rectifier tube. So on your recommendation, I'd like to get a 47uF, 450 volt to replace it.
If I order one through Madison, what exactly do I specify other than 47 uf 450 vac?
Thanks!

If you look at the pin diagram in the data sheet (the pin numbers are looking at the bottom of the socket, btw), you'll see that the first cap will be connected to Pin 8 (typically, or it could be pin 2). Check to see if that's the cap you mentioned.

If you can post a pic it would be helpful but I assume this is one of the ubiquitous SE EL84 Chinese amps. If so, it will have a choke (small transformer mounted underneath) after the first cap and then a second cap. The second cap can be larger than 47uf.

I suggest you get a cap rated at 105 degrees for 10,000 hours. Any major brand - Nichicon, Panasonic, etc. Make sure to check the dimensions of your stock cap so whatever you buy will fit.

https://www.digikey.com/products/en...tity=&ColumnSort=0&page=1&stock=1&pageSize=25

I know Madisound is local to you but I took a look at their website and they don't seem to sell any high voltage electrolytic caps since they mostly sell speaker-related stuff. I say "seem" because the search function on their site sucks. Most of the electrolytic caps they sell are non-polar, which are for speaker crossovers and rated at much lower voltages. Of course they have ridiculously priced boutique caps too if you want to spend more for one cap than you did for your amp.

I usually order from Digi-Key, which is a major supplier and close to you too, in Minnesota.
If you're just ordering a few parts your total expense will be much higher due to shipping costs. Here's how to get free shipping from Digi-Key:
http://www.audiokarma.org/forums/in...hipping-on-parts-orders.739513/#post-10018562