earthsled

Gates Sta-Level M5167 - power transformer questions
« on: July 09, 2019, 09:28:00 PM »
Hi folks!

I'm working on an original Gates Sta-Level compressor. I believe the PT might be fried, but I wanted a sanity check before going down the road of replacement.

This unit was powered on by the engineers at the studio for testing. Unfortunately, they didn't notice the rectifier tube had broken glass. When powered up, the engineers reported a "burning smell" and that the unit was not passing signal.

Now that I have the Sta-Level on my bench, I found that there was an over-rated mains fuse installed. It had a 3A slow-blow instead of the 2A fuse specified in the manual.

Fearing the worst I removed all the tubes and gave it about 50V AC from my Variac. At this voltage, the unit was drawing about 1.25A. I didn't increase the voltage past 50V. After a few minutes, the PT started to get warm. Things are NOT looking good so far!

After powering the unit down, I took some resistance measurements from the PT and the choke. Here are my results:

Primary: 10 ohms
High Voltage Secondary: 300 ohms
5V Heaters: 0.3 ohms
6.3V Heaters: 0.2 ohms

Choke: 400 ohms

My best guess is the choke survived, but let me know if the resistance seems high to anyone. Also, I wanted to verify that 1.25A is an unusually high current draw for this PT without any tubes installed. Again, I suspect the PT is gone, but I didn't want to overlook anything.

Thanks in advance for your help!




mjrippe

Re: Gates Sta-Level M5167 - power transformer questions
« Reply #1 on: July 09, 2019, 10:47:05 PM »
A dead short on C12B might cause problems, but with all the tubes out I think you have found the problem.

rackmonkey

Re: Gates Sta-Level M5167 - power transformer questions
« Reply #2 on: July 09, 2019, 11:40:14 PM »
The DCR measurements are about right for all windings on the PT.  You obviously don’t have a fully open winding anywhere, but that doesn’t mean you might not have some burned-through insulation on one or more.
Whether you think you can or you think you can't, you're probably right.

PRR

Re: Gates Sta-Level M5167 - power transformer questions
« Reply #3 on: July 10, 2019, 12:05:47 AM »
Sure looks to me like the PT for a Fender DeLuxe would work. Maybe a large (500r 10W?) resistor in series with the choke to bring-down the overvoltage.

You may be a part-Amp high on the 6V winding, but that won't die quickly. And the DeLuxe PT can be found cheaper than any other similar PT.

earthsled

Re: Gates Sta-Level M5167 - power transformer questions
« Reply #4 on: July 10, 2019, 12:53:55 AM »
Thanks everyone for your replies!

mjrippe - Resistance on the filter caps is looking good (all are testing the meg-ohms). Needless to say, a shorted cap has often been the culprit for power supply failures in the past.

rackmonkey - Great point about the "burned-through insulation" inside the PT. I agree that the DCR on the windings is testing suspiciously normal.

PRR - Awesome suggestion about the Fender Deluxe PT for a replacement! I believe the Hammond part number is 290BX for their Deluxe PT replacement. It looks like the price is around $78 (very affordable). End bells would be needed for mounting.

Other possible replacements are available from Sowter and Edcor. Sowter's replacement (model 9880) is very nice, but quite expensive at about $240 in US dollars. Edcor makes a suitable replacement (model XPWR221) for about $61.

Also, I recently received a reply from Phil at Retro Instruments about the PT. He says that the original was a standard issue made by Triad (model R-10A). Apparently these turn up on eBay from time to time. It might be worth the wait - especially if the footprint matches up. I'd love to avoid drilling new holes for mounting if possible.

EmRR

Re: Gates Sta-Level M5167 - power transformer questions
« Reply #5 on: July 10, 2019, 08:18:39 AM »
I've seen this on similar tube gear, certainly a shorted PT winding.  Sorry. 

One SA-39 I rebuilt with a correct  NOS Triad PT (replacing a shorted one) maybe 7-8 years ago was left on 24/7 at the owners studio with no maintenance checks on tubes or anything else, and it ate that replacement PT too once the rectifier went, even with the correct fuse. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

rackmonkey

Re: Gates Sta-Level M5167 - power transformer questions
« Reply #6 on: July 10, 2019, 10:25:45 AM »
I've seen this on similar tube gear, certainly a shorted PT winding.  Sorry. 


Doug, so for my future troubleshooting, a shorted winding in this case can sometimes not show as open when measured for DCR? Is it like I theorized as melted through insulation (and could thus be intermittent)?
Whether you think you can or you think you can't, you're probably right.

mjrippe

Re: Gates Sta-Level M5167 - power transformer questions
« Reply #7 on: July 10, 2019, 10:35:38 AM »
Doug, so for my future troubleshooting, a shorted winding in this case can sometimes not show as open when measured for DCR? Is it like I theorized as melted through insulation (and could thus be intermittent)?

Not Doug, but...

A short would show as zero ohms, a partial short (likely here) may show as lower than expected ohms.  And yes it could be intermittent, only arcing over once the voltage is high enough.

Mike

EmRR

Re: Gates Sta-Level M5167 - power transformer questions
« Reply #8 on: July 10, 2019, 11:20:16 AM »
Doug, so for my future troubleshooting, a shorted winding in this case can sometimes not show as open when measured for DCR? Is it like I theorized as melted through insulation (and could thus be intermittent)?


I've seem DCR look correct but with a short to the case, etc. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

rackmonkey

Re: Gates Sta-Level M5167 - power transformer questions
« Reply #9 on: July 10, 2019, 03:59:58 PM »
Okay thanks both. I've seen full shorts and funny behavior with normal readings, but my theory about burned through insulation was just that. Good to have your experiences in my pocket.
Whether you think you can or you think you can't, you're probably right.


earthsled

Re: Gates Sta-Level M5167 - power transformer questions
« Reply #10 on: July 10, 2019, 06:45:55 PM »
Quote
One SA-39 I rebuilt with a correct  NOS Triad PT (replacing a shorted one) maybe 7-8 years ago was left on 24/7 at the owners studio with no maintenance checks on tubes or anything else, and it ate that replacement PT too once the rectifier went, even with the correct fuse.

Yikes! Maybe the NOS Triad PT is not the best choice? Or, perhaps a lower fuse rating would be advisable? I guess it's not too uncommon for the PT to be "eaten" if the rectifier fails or gets shorted.


EmRR

Re: Gates Sta-Level M5167 - power transformer questions
« Reply #11 on: July 11, 2019, 08:12:49 AM »
Yikes! Maybe the NOS Triad PT is not the best choice? Or, perhaps a lower fuse rating would be advisable? I guess it's not too uncommon for the PT to be "eaten" if the rectifier fails or gets shorted.

It was the correct stock replacement, but those are frequently replaced with the next mA size up; then you have initial B+ 50V higher and have a different problem (cap rating) to compensate.   
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

earthsled

Re: Gates Sta-Level M5167 - power transformer questions
« Reply #12 on: July 22, 2019, 07:54:25 PM »
Well, I'm still kicking around ideas for the best PT replacement. Ideally, a NOS Triad R-10A will turn up, but I guess I can't keep my client waiting forever...

One more PT model I'm considering is the Hammond 270FX (spec sheet attached). The mounting dimensions are very close to the original footprint. I'll have to turn it 90 degrees, but I might get away with using the original mounting holes.

I'm thinking I will definitely have to prop it up on a collection of washers or thick spacers so I can route the wires though the original entry hole. The unique thing about the Triad PT is that it only had one exit hole for both primary and secondary wires. Thus, the Sta-Level only has one entry hole to match. Internally, the choke mounts on the opposite side of the PT, so there's not much room for a second entry hole or finagling with the mounting hole positions.

With the 270FX, the high-voltage secondary is 25V higher than the original (at 550V rather than 525V). EmRR mentioned that a B+ that was 50V higher might be a concern for cap ratings. This particular Sta-Level has the original can-style caps replaced with axial Sprague Atom types rated at 450V. Am I in danger of destroying the caps with the extra 25V?

EmRR

Re: Gates Sta-Level M5167 - power transformer questions New
« Reply #13 on: July 23, 2019, 07:23:34 AM »
90º orientation from original is probably bad idea.  May orient max hum into audio.

I’d look at UTC Thordarson Kenyon Haldorson etc etc and see what vintage options exist besides the Triad, more likely to be exact fit.  The Triad will probably also show up within 1-2 months. 

Higher voltage in the Hammond can be dropped with resistor change, as it could in an SA-39.   SA-39 is a 700V secondary, you are nowhere near the same threshold. 

It does not appear I have an R-10A in my stock. 
« Last Edit: July 23, 2019, 10:14:28 AM by EmRR »
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde


 

Related Topics

  Subject / Started by Replies Last post
9 Replies
2864 Views
Last post June 27, 2016, 07:38:04 AM
by beatnik
gates sta level pops

Started by rove « 1 2 » The Lab

22 Replies
4524 Views
Last post July 19, 2005, 04:34:58 PM
by CJ
27 Replies
12673 Views
Last post August 10, 2012, 10:13:27 PM
by rafafredd
4 Replies
2568 Views
Last post May 13, 2010, 10:40:33 AM
by takisti