The Tale of Two Standel Custom 15's

Michael Brebes · Post by **Michael Brebes** » 16 Feb 2019 9:36 am

Chassis #1: The second preamp module is made and wired in. The power cord, which was a 2 prong with 18ga zip cord, has been replaced with a real power cord. The 2 prong jack on the back has been replaced with a 3 prong connector. The wires for the optocoupler are still left hanging. I will test and decide just how to attach it in the circuit. It's a good thing I redid the tremolo approach because the tremolo transformer is bad as well. No matter which leads I measure between they all measure the same resistance, which is not a good sign.

Michael Brebes · Post by **Michael Brebes** » 16 Feb 2019 11:22 am

Chassis #1: Didn't notice before when I hooked the amp up to the speaker but the output is distorted unless the scope probe is on one of the grids on the power tubes. On further investigation I found that the negative bias for the grids was attached to nothing. The two resistors had been removed. Reinstalled and the power amp now works with the scope probe off. Found that the optoisolator works fine being attached to the wiper of the volume pot. By test found that the orange OT wire has best power transfer for an 8 ohm speaker and that the yellow is a good match for a 16 ohm, which I believe Jerry told was the impedance of the D130 in his cabinet. Had to use a 12AU7 or 12AY7 in the phase inverter circuit to get the gain to a usable range.

Next, solder in the feedback wire and the yellow wire for the speaker. Then put in a new set of tubes and it should be done! Then on to finishing Chassis #2.

Jerry Roller · Post by **Jerry Roller** » 16 Feb 2019 12:11 pm

Michael, I appreciate you fixing my amp very much and I donâ€™t want to cause you any extra work, however, most of my JBL peakers are 8 ohm and you mention the use of one wire to use an 8 ohm and a different wire for a 16 ohm speaker. Does that mean it can be set up for an 8 ohm? If so, that would be great. If it involves additional problems donâ€™t worry with it.
Thanks,
Jerry

Michael Brebes · Post by **Michael Brebes** » 16 Feb 2019 1:18 pm

Chassis #1: Had to move OT to speaker to Black/Wh wire because the high voltage was pulling down and, with the new tubes, the output was about the same as with the old tubes. Measured output at about 35 watts RMS into 16 ohm load. Had too much hum and found a missing capacitor on the negative bias voltage. Finished attaching the remaining optocoupler wires and feedback wire. All is working with a new set of power tubes and a new 12AU7/ECC82 in the phase inverter. Tested one more time and all is well. Ready to ship back to Jerry!

Michael Brebes · Post by **Michael Brebes** » 17 Feb 2019 2:30 pm

Chassis #2: Powered up with power tubes and it passes signal but only about the equivalent of 5 watts is coming out of the amp. Signal levels from the phase inverter look okay. All voltages at the power tubes look okay. I did notice that the power amp schematic is a bit different. Will have to draw it out to see what I've got. At this point I am starting to suspect the output transformer as being bad. Will "hotwire" the one from an S100V I have to see if that tells me anything. One bit of good news is that the tremolo oscillator circuit is working fine. Still also need to build the second input module and wire it in.

Michael Brebes · Post by **Michael Brebes** » 18 Feb 2019 5:23 pm

Chassis #2: Found that the wires going from a 10K current limiter resistor to Grid 1 on both tubes was poor or intermittent at best. Since the wires soldered to the terminals underneath I just cut them off and replaced them. Now the power amp is happily chugging away.

Still need to build the second preamp module and install.

Michael Brebes · Post by **Michael Brebes** » 19 Feb 2019 8:32 am

Chassis #2: Built and installed the second preamp module. The tremolo optocoupler is wired in and the tremolo is fully functional. Still waiting for a 12AU7 tube but it just means I have to run the input volume at 1 or 2 for now. Haven't decided whether I am going to install the 3 prong accessory power plug in this chassis or not. Here is the completed chassis (for now at least).

My thoughts after completing the two chassis repairs?
I have repaired a number of these hybrid amps and have had to replace one, two, maybe even three modules, but I have never had to replace all five before. It goes to show how someone can cause more damage than was previously there by blindly going into these amps, especially when they think it's just another tube amp. These are unique. The best approach is always to document the circuitry before you move anything. When I started tackling this project, I thought I would look at other output tube options but there really aren't any other options without completely overhauling the design of the power amp. The voltage doubler power supply has its limitations which compounds everything else.

Michael Brebes · Post by **Michael Brebes** » 21 Feb 2019 7:45 am

Listening to both amps got me realizing that the oldest chassis #1 has a lower output than the newer chassis #2 and slightly thinner tone. I had previously measured both output transformers and the one in Chassis #1 does not measure the same as Chassis #2 or my S100V. Replacing all the out-of-spec resistors in the power amp made no difference, so it has to be the output transformer. Jerry has yet a third non-working chassis which has the correct output transformer so that transformer is on its way to me. Almost there with both amps.

Michael Brebes · Post by **Michael Brebes** » 28 Feb 2019 5:47 pm

Chassis #1: Replaced the output transformer with the one from the third chassis and the amp sounds great driving my 8 ohm JBL 15" speaker. It will get boxed up tomorrow morning, along with a Standel Artist Bass amp that came in today and was able to fix today. Both chassis are working and this project is now officially done.

P.S. Jerry is going to send me his third chassis, that is missing most of the modules and now an output transformer. I will build it back up and use it as my test chassis for converting from 6GW6/6GT5 tubes to standard 6L6GC power tubes. I will start a new forum topic when I finally decide to start that project!

Jerry Roller · Post by **Jerry Roller** » 28 Feb 2019 6:33 pm

Genius at work!!!
Jerry

Michael Maddex · Post by **Michael Maddex** » 1 Mar 2019 9:04 am

Jerry Roller wrote:Genius at work!!!

Ditto that!

Michael, good job! Thanks for telling us the tale. It is most interesting.

Jerry Roller · Post by **Jerry Roller** » 7 Mar 2019 3:34 pm

I received the Standel Transistorized Custom 15 chassis back from Michael yesterday. I didn't have time to hook it up and try it until today and I am truly amazed. It sounds terrific and is absolutely quiet with zero hum with Bill Lawrence 710's and volume way past where I normal play. The tone is crystal clear. Michael totally built new modules to replace all that were in the amp. I had no idea that Michael or anyone for that matter was that good and he treated me more than fair. I tried for several years to find someone who could fix this amp but two others failed, only making it tougher on Michael as it was completely apart when I sent it to him. I am sure there are enough Standels in existence that need repairs that Michael should have all the work he could possibly want and I absolutely recommend him 100%. I am so thankful to Michael for fixing it for me. I bought it brand new in around 1963 and I have a sentimental attachment to it. We had not been married long and at $400.00 it was a real struggle for us to buy it and I am thrilled that I can once again use it. I am amazed at what Michael was able to do. Both channels work which includes a tremolo channel that I may never use but I am happy both channels work as they should. Thank you Michael Brebes!!!
Jerry

Michael Brebes · Post by **Michael Brebes** » 8 Mar 2019 3:43 pm

You are welcome. Glad I could help get rid of the frustration you've had for such a long time with that amp. Enjoy. You should post a pic of your amp when it's all together.

Jerry Roller · Post by **Jerry Roller** » 11 Mar 2019 9:05 pm

Michael, the amp sounds great. Itâ€™s 54 years show but I kinda like the look. I may redo the Tolex and grille sometime but for me it is all about the sound and it has it.
Thanks again Michael!!

Michael Brebes · Post by **Michael Brebes** » 12 Mar 2019 6:50 am

Looks good! Will post a pic of Chassis #2 in its cabinet.

Jerry Roller · Post by **Jerry Roller** » 12 Mar 2019 7:22 am

Mine sounds wonderful. I bet you already recovered yours?
Jerry

Brett Lanier · Post by **Brett Lanier** » 12 Mar 2019 9:52 am

So great to read about your amp being fixed, Jerry! I know you've been looking for the right person to do it for a while.

I'm cuckoo for Standel amps. I played a '65 solid state Custom XV for about 4 years, and still bring it around as a backup. Got a 50L15 a little over a year ago (which came from Hank Thompson's estate), it's easily my favorite steel amp.

Michael Brebes · Post by **Michael Brebes** » 12 Mar 2019 11:36 am

Here's pics of Chassis #2 in the cabinet. It's heavy with that 15" JBL in there. I opted not to replace the covering because of how unique and unavailable it is. I did find a source for the grill cloth, which has a 2 yard minimum. It's the same grill cloth that was used by Sunn amplifiers back in the sixties. I know because I have one.

Jerry Roller · Post by **Jerry Roller** » 12 Mar 2019 2:46 pm

Michael, do you re-cone speakers? Does your chassis 2 sound good?
I guess you noticed my cabinet is pretty rough, a little worse than yours but I donâ€™t mind. I might recover it sometime. We could split that 2 yard minimum order if you wish.
Jerry

Michael Brebes · Post by **Michael Brebes** » 12 Mar 2019 6:27 pm

Jerry, yes I can recone a lot of speakers as long as the recone kit is available. Just did an EVM15B a week ago.

If you are interested in replacing the grill cloth I could split it with you. The amp covering is very thin compared to available tolex amp coverings available today. Some of the cabinets are really hard to recover with the new stuff because of the sharp angles that can't be done with the thick stuff.

Notice how big the magnet is on my 15" speaker. It makes the amp pretty heavy.

George Seymour · Post by **George Seymour** » 30 Oct 2023 8:12 am

Michael Brebes wrote:Here's pics of Chassis #2 in the cabinet. It's heavy with that 15" JBL in there. I opted not to replace the covering because of how unique and unavailable it is. I did find a source for the grill cloth, which has a 2 yard minimum. It's the same grill cloth that was used by Sunn amplifiers back in the sixties. I know because I have one.

Thank you Micheal for selling this to me..absolutely incredible steel guitar amp

George Seymour · Post by **George Seymour** » 30 Oct 2023 3:45 pm

Great match for the wrap around

The Steel Guitar Forum

The Tale of Two Standel Custom 15's

Cudo's to Michael Brebes

Standel 82L15V