Another Golden Tube SE-40 adventure

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Marty Ackerman

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Another Golden Tube SE-40 adventure
« on: 19 Sep 2018, 08:53 pm »
I recently received a broken SE-40 amp.  It had been in a basement for a few years after malfunctioning until I ended up with it.

I found the Sonic Craft mod after doing some research and decided to get the REL+ kit in hopes of getting her up and running. The kit was really well put together and documented.  It was a pretty simple, if painstaking job. The hardest part is removing so many components without causing damage to the board or grinding your teeth to dust. At this point, I've installed the modification and I have some new 6sn7's on the way.  In the mean time, I tried to bias the amp with the existing 6sn7's and some 5881 power tubes I had. Here's where I have some issues.

There is a separate bias pot for each tube, which I assume means I can use non-matched tube sets, correct?

I'm getting 0 volts when trying to bias v8. I assume that means that I've burnt out r25? I might have gone over the rating or rotated the knob all the way in the wrong direction to start the bias  :duh: - it's been a few days, I can't remember exactly. I did try with a different tube and still 0 volts. The rest of the tubes are fine.

I've got some 5881's, 6l6's, and a set of KT66's, though I'm not sure which manufacturer at the moment.  If I want to try tubes other than the 5881, how do I know what the bias reading should be? Am I always aiming for the .605v range, or does it vary from tube to tube?

Thanks in advance for your knowledge and help on this.  I'm excited to hear it.



Jeff

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Re: Another Golden Tube SE-40 adventure
« Reply #1 on: 20 Sep 2018, 11:19 pm »
Marty,

Welcome to my circle.

The REL+  underwent a couple of rolling revisions over the past 15 years.  When did you purchase your kit?

If R25 is gone, it will appear cooked (or worse) :wink:  R25 has nothing to do with V8.

A single detailed pic of the bottom of the amp (cover off of course), would be the best place to start.

Jeff

Marty Ackerman

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Re: Another Golden Tube SE-40 adventure
« Reply #2 on: 21 Sep 2018, 02:46 pm »
Thanks for the reply!

I purchased the kit on 9/6/2018 - just a couple weeks ago.

I was looking at a schematic I found online, but it was for one channel only - it seems that the resistor I was suspecting was actually r45? Either way, those new resistors looked nice and new and measured 11.1 ohms.

Here's a pic of the current situation.


Jeff

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Re: Another Golden Tube SE-40 adventure
« Reply #3 on: 21 Sep 2018, 08:14 pm »
Yes Sir, you must be Derril Seller's tech, or vice versa... :dunno: :lol:

Your pic is far too small for me to see what is going on.  For potentially better, and faster service, you could send a pic to the contact link on our website.

Since you are some kind of tech, this may sound silly, but be sure you have a good joint on both sides of the board regarding R45.  Also check the voltage drop across R45.  This will negate any potential issues with your biasing harness.

Did you receive any instructions?

You may use any of those tubes as long as they will handle 500 plate volts, and 30W of dissipation.  They will all bias the same.  No true 5881 will do that.  Few true KT66s will do that.  Long term anyway.

Marty Ackerman

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Re: Another Golden Tube SE-40 adventure
« Reply #4 on: 21 Sep 2018, 08:34 pm »
You've got the one.  I'm my own "tech" - I enjoy learning and working on these things more than listening sometimes, but I have no EE degree or anything.

I measured voltage drop across all the bias resistors and got about .600v EXCEPT across r45, which was 0. Resistance between the pads on the component side of the board was 11.1 ohms, but I haven't removed the board and checked the same from the socket side. I suppose I could re-flow the solder on any iffy-looking parts as well.

Here's a link to the pic that should be able to blow up much larger: https://imgur.com/a/hHHTHUZ

I'll also try sending to the contact email.

I really appreciate you taking the time to look at these.

Jeff

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Re: Another Golden Tube SE-40 adventure
« Reply #5 on: 21 Sep 2018, 10:43 pm »
The image Derril sent was detailed.  It appears that several joints could stand to be re-flowed.  You will definitely need to check the other side of the board.  Be sure to review the instructions again.  Especially the bias.  If one of those tubes takes off, it can cause immediate damage undetectable by a tube tester.  I mention the instructions only because you appear to have missed a few things.

Are you using the solder we provide?

Marty Ackerman

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Re: Another Golden Tube SE-40 adventure
« Reply #6 on: 22 Sep 2018, 01:39 pm »
I re-flowed solder on both sides of the board last night. I am using the provided solder.

When I put her back together and re-biased, I still had the same issue. The amp was still on while I looked around and rechecked bias etc and suddenly I heard a little "tick" sound and the tube lit up!

I biased the whole amp, turned it off and let it cool.  After a while I turned it on again and that same v8 tube took about 10 minutes to heat up. It's odd behavior, but the amp works and sounds great.

Any idea what could cause this? Also, I re-checked and read the instructions again - I can't find any steps that I missed. You mentioned that there were some things I missed - could you give me an idea of what those might be?

Jeff

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Re: Another Golden Tube SE-40 adventure
« Reply #7 on: 22 Sep 2018, 07:44 pm »
Since you have ruled out the tube, I can only assume the socket.  When we do in-house installs/mods, socket service is automatic.  We do not automatically perform it on $50 repairs.  It use to be optional, but customers felt it was worth $25.  Even though 85% of the amps we would see needed it.  Cleaning and tightening 68 two tongue pins is $25 the hard way, and I'm going to have to talk them into it :o :roll:

I merely mentioned rereading...  It is impossible for me to know what you "might" have missed.  It is merely one page front and back.  However, I noticed you mentioned, I might have gone over the rating or rotated the knob all the way in the wrong direction to start the bias, Am I always aiming for the .605v range  This is contrary to paragraph 8.  That paragraph also lists an email address in which to contact me if you have any questions or problems.  These are small potatoes.  But, it appears that you did not follow the spacing/clearance laid out in section 6.  This is for much needed ventilation.  Now that the leads are trimmed, it will not be possible  :(  There are a couple of other things, but they do not appear as if they will be giving you trouble.  No harm, no foul.