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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 18th June 2017, 08:12 PM   #11
Rundmaus is offline Rundmaus  Germany
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Quote:
Originally Posted by Nikon1975 View Post
R2 should be 150K not 150 ohm. if it was 150 it tried to dissipate almost 1000w
+1

R2 is a bleeder resistor for the 1st filter cap, it has the full raw B+ across. It needs to be 150k.

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Rundmaus
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Old 20th June 2017, 02:48 PM   #12
Tubelab_com is online now Tubelab_com  United States
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Quote:
maybe itīs available only to members.
There are no "members." Its available to everyone as all of my material.

Yes, R2 is the wrong value and would fry in a flash. It needs to be a 150 K ohm 3 watt part. R4 must also be 150 K ohm or there will be more bad parts.

It is possible that the rectifier tube got damaged by attempting to pass 3 amps or so of current.

Quote:
Maybe the SS/Tube switch was ON and the SS diodes took the surge.
I doubt it. R2 would have instantly vaporized, or the fuse should have blown. If you are on US power the fuse should be 2 amps, 1 amp on 240 volt power.
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Old 20th June 2017, 02:53 PM   #13
Rundmaus is offline Rundmaus  Germany
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Quote:
Originally Posted by Tubelab_com View Post
It is possible that the rectifier tube got damaged by attempting to pass 3 amps or so of current.
Surprises me that the tube took that near-short without a flash and a bang. I have a tube rectification supply that slightly pushes the spec boundaries - took a while to select a few tubes that work without flashing over...

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Rundmaus
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Old 20th June 2017, 04:18 PM   #14
JMFahey is offline JMFahey  Argentina
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Please post a readable schematic, I am unable to open the Tubelab page (page not found), maybe itīs available only to members.
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Originally Posted by Tubelab_com View Post
There are no "members." Its available to everyone as all of my material.
Thanks.
I clicked http://www.tubelab.com/images/Assemb...e_noCFB.jpg%5D and page answers:

Quote:
Nothing Found

Apologies, but no results were found for the requested archive. Perhaps searching will help find a related post.
Hence my comment
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Old 25th June 2017, 12:39 PM   #15
capitanalga is offline capitanalga  Spain
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Quote:
Originally Posted by Tubelab_com View Post
I doubt it. R2 would have instantly vaporized, or the fuse should have blown. If you are on US power the fuse should be 2 amps, 1 amp on 240 volt power.
Hi! thanks for the explanation. I don't know how could I make a 10^3 ohm mistake..... I checked values 10 times, looks like it was not enough. Anyway, happy to know where the problem is.

Regarding to the fuse, it has blown.. I was trying with 1A first and it blew, then put a 2A and there I got some second of work before R2 blew. I'm using 230V power (europe) so I should go for 1A? can I try higher values (maybe 1,5 or 2A) in case it blows?

thx!
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Old 4th July 2017, 05:27 PM   #16
capitanalga is offline capitanalga  Spain
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Hi! Finally I soldered the correct resistor But unfortunately I get no sound at all and one of the kt88 does not even glow

What should I check? Where do I have to measure? What am I doing wrong??

Thank you!!!
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Old 4th July 2017, 07:04 PM   #17
rayma is offline rayma  United States
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Quote:
Originally Posted by capitanalga View Post
I get no sound at all and one of the kt88 does not even glow. What should I check?
With newly built hardware, there could be several independent problems, plus problems caused by
other problems (cascading failures) after turning it on for the first time. It's best to measure
the resistors with a meter, both before soldering, and after a failure. Until you know more about
circuits, just check everything you can, all the parts and all their connections. A dark filament will
usually be due to a bad or wrong filament connection. After checking everything, if possible test
the rectifier tube in a tube tester, or substitute a known good one. It could have been damaged.

Last edited by rayma; 4th July 2017 at 07:08 PM.
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Old 5th July 2017, 01:54 AM   #18
cbutterworth is offline cbutterworth  United States
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Have you tried completing the SSE checkout:

<a href="http://s69.photobucket.com/user/Ty_Bower/media/Simple%20SE/Checkout/ohm00.jpg.html" target="_blank"><img src="http://i69.photobucket.com/albums/i43/Ty_Bower/Simple%20SE/Checkout/ohm00.jpg" border="0" alt=" photo ohm00.jpg"/></a>

Charlie
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Old 5th July 2017, 02:47 PM   #19
w5jag is online now w5jag  United States
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As to the power tube not lighting up - check that the tube socket is Installed ( oriented ) correctly. If it is oriented correctly, then the tube is bad.

As to no sound - lots of potential causes.

It looks to me like the rectifier tube you are using is the Sovtek "5Y3GT". These are neat looking tubes, but I have to tell you that I have found them to be quite fragile in my experience. First off, they are not a 5Y3 type - they output voltage about like a 5V4, but can only supply current about like a 5W4, in my experience. Second, if that was the tube that was in place when you smoked the bleeder, it is almost certainly fried as well. Third, if by some miracle it didn't fry when the bleeder fried, the current drain of two 6550 / KT88's will fry it in short order.

Just my $0.02.

Win W5JAG
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Old 5th July 2017, 06:59 PM   #20
capitanalga is offline capitanalga  Spain
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Quote:
Originally Posted by rayma View Post
With newly built hardware, there could be several independent problems, plus problems caused by
other problems (cascading failures) after turning it on for the first time. It's best to measure
the resistors with a meter, both before soldering, and after a failure. Until you know more about
circuits, just check everything you can, all the parts and all their connections. A dark filament will
usually be due to a bad or wrong filament connection. After checking everything, if possible test
the rectifier tube in a tube tester, or substitute a known good one. It could have been damaged.
- Rectifier tube has been checked (pin 2 and 7 are connected) plus it glows when turned on. --> Can this guarantee that tube is operational?


Quote:
Originally Posted by w5jag View Post
As to the power tube not lighting up - check that the tube socket is Installed ( oriented ) correctly. If it is oriented correctly, then the tube is bad.

As to no sound - lots of potential causes.

It looks to me like the rectifier tube you are using is the Sovtek "5Y3GT". These are neat looking tubes, but I have to tell you that I have found them to be quite fragile in my experience. First off, they are not a 5Y3 type - they output voltage about like a 5V4, but can only supply current about like a 5W4, in my experience. Second, if that was the tube that was in place when you smoked the bleeder, it is almost certainly fried as well. Third, if by some miracle it didn't fry when the bleeder fried, the current drain of two 6550 / KT88's will fry it in short order.

Just my $0.02.

Win W5JAG
- What rectifier should I use, I have checked on several configurations other people have chosen and this is why I chose kt88 + 5Y3GT.

- KT88 is fully operational, I have changed position of KT88 and the one that was not glowing now glows. So there is someting about the socket..

- Plus, if I get really close to the speaker, I can hear a really really low hum in one speaker but not in the other..

What else? Should I take the valves out, turn the amp on and do some measurements?

THX!!!
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