MASCO MAP 15 - need help install 3 prong ac cord

[sig]

Might Have Found Problem, please help me Experts.. THANKS!

Please read and let me know your thoughts, Prairie Dawg got me started on a systematic troubleshooting process and I may have found the issue on this OLDER than dirt amp. It's cool though and I can't wait to finish it. Thanks for all the help thus far everyone, you've got me off of facebook, thank GOD!.

Prairie Dawg, et al... No rectifier tube Power Transformer Voltage Measurements (AC)
The (Greens) = 7.15v
The (Yellows) 5.48v
The (Reds) to Ground = approx 358v each red lead
*** I noticed a third lead hiding under the two RED leads, and it is wired directly to the common ground surrounding the 5Y3 rectifier tube. The 16uf caps negative sides are also wired to this same ground, positive sides to the choke. PLEASE look at the Power Transformer on the schematic, you will see that ground wire to ground in the graphic. I believe (may be wrong and need confirmation) that this is causing my problem when I ground the chassis as I'm creating a direct path to the AC from the (Red) 358v per lead, wires.

Notes: (1) I started working my way through the signal flow. I ordered a couple NOS 5Y3tubes today should be in next week, I'm hesitant to use my last one right now although I believe it will work with the ground wire lifted. I'm going through the schematic, one resistor, cap at a time while looking at the chassis to make sense of the mess. Some intial findings this far:
(2) My wiring of pin 4 & 5 of the 6L6 tubes is reversed from what the Schematic shows. Is this an issue?
(3) Schematic shows the Output Grid Resistors #29 and #30 are supposed to be 500K but both mine read 1MoHm. Is this an issue? Color codes match Green > Black > Yellow.

[Jazz P Bass]

How did you miswire the 6L6 pin 4 & 5?
Pin 5 is the grid pin.
This is where the low voltage signal comes into the tube.
Pin 4 is the screen grid.
It should be slightly lower Vdc than B+.
As to the hidden transformer winding: look at the schematic.
The power transformer secondary is center tapped to ground.
Off of this center tap you have two outside windings which go to the rectifier.
It is wired properly if both windings measure the same resistance in relation to the center tap.

[Prairie Dawg]

Your measurements look good. Your green is the filaments and with no tubes you're about right. Expect it to drop right in the sweet spot with a full complement of tubes. Your yellow is about right as well without a load. You can set it up with diodes if you like, or if there's something wrong with the 5v circuit. Your B+ picks off the 5V winding so with a rectifier tube on board you'll see the 5v AC as well as about 350v DC going out to the output transformer and then back to pin three on the power tubes. If you get this far and install a set of power tubes make sure the speaker is connected. I agree with JPB-you're probably looking at the center tap going to ground.

[sig]

Thanks Prairie Dawg. It'll work with all tubes as long as I don't connect that green ground wire on the new power cord, at least it did.

[Prairie Dawg]

You might, as the brother suggested, have a hot chassis. It's worth checking it with your multimeter to see if line voltage is getting out on the chassis.

[g1]

Better double check and clear up what you meant about pins 4 & 5 of 6L6's.
As far as the hot chassis, it's sounding sort of like this: http://music-electronics-forum.com/t25172/
Try plugging it in with ground connected but no rectifier tube installed.

[52 Bill]

*** I noticed a third lead hiding under the two RED leads, and it is wired directly to the common ground surrounding the 5Y3 rectifier tube. The 16uf caps negative sides are also wired to this same ground, positive sides to the choke. PLEASE look at the Power Transformer on the schematic, you will see that ground wire to ground in the graphic. I believe (may be wrong and need confirmation) that this is causing my problem when I ground the chassis as I'm creating a direct path to the AC from the (Red) 358v per lead, wires.

I'm sorry, but from this statement it's obvious that you really don't understand how transformers work and more importantly how ac primary wiring works. Before you do anything else with the tubes and the rest of this amp, you need to find and fix the problem with the ac ground and the hot chassis. Even if you have a working amp that gives you the sound of God and thunder, if it kills you it really wasn't worth the money you saved by not fixing it correctly. Three or four of us have already warned you about this, but you either don't get the seriousness of the problem or you don't care, in which case nobody here should be giving you any advice how to continue.

[sig]

52 BILL et al...
Don't be sorry, believe me I listen and learn from every reply I've received thus far. I am not going back to a working amp that has the potential to kill me. And yes, I'm a novice at this stuff and am learning.

Again everyone, I appreciate you all helping me! I'm not playing through this amp, in fact right now, I'm awaiting receipt of a solid state rectifier plug as was recommended to test next to potentially isolate the problem to the PT.

I wear 10KV gloves when the amp is plugged in!

Paul

[sig]

Here's a Situation Report:
1. Regarding my claim that I thought Pin 4 & 5 were reversed on the 6L6s, I was wrong, I was reading the tube numbers backwards from underneath the chassis. Like Phil said when he lost the US Open, "I'm an idiot"..
2. I dicovered that I had the polarity backwards on capacitor #16, I just fixed that problem.
3. I received to NOS KENRAD 5Y3 tubes, but I also ordered 2 octal plugs that have diodes wired in them. I'm going to wait until the diode plugs arrive and try them first.
4. The .01mf caps on the schematic numbered 12-15 I replaced with Sprague Orange Drops 600v 103J. The schematic lists polarity symbols for these caps, from what I understand these orange drop caps should work but aren't polarized. Should this be a concern? I do have other caps, some malory .01mf 600v but they aren't polarized either. I'm not sure caps of these values are made polarized and I don't know if it matters. Appreciate any advice and if I should get polarized caps for this, I'd grately appreciate referal to a source.
5. The amp originally called for 6L6GA tubes according to the chart with the schematic. I've got a matched set of 6L6EH Electro Harmonix. I read that the new 6L6 tubes are a huge upgrade to the 1940s 6L6GA tubes of the past and somewhere I read that I might want to step up the filter caps from what the schematic reads "16MF 450V" to a greater value in the 500V range. I also read by doing so might decrease the noise level. I'm considering this, thinking about 30MF 500V, to replace caps number 6 & 7, and perhaps 20MF 500v for cap numbers 8a & 8b.

On a cosmetic note, I ordered a new leather handle for the amp, the old one is missing. The hardware on the amp is original and in good condition, but I don't know how to remove the hardward to put the new handle on. There's no bolt on the inside of the cabinet that I can see or feel, and the bolt heads don't have any groves for a phillips or straight head screwdriver. I don't want to damage it, but I think it's in some sort of a rivited lock or something. I was considering to drill through the bolts or grind them down with my dremel. The handle looks like what you might see on a 50s Tweed Deluxe or Champ.

Thanks!

Paul

[Dave Curtis, dB AudioTech]

WRT the handle, it's probably attached with split rivets; picture a short nail where the shaft is split down the middle. When driven in, the 2 sides of the rivet spread out into the wood. You'll have to carefully pry them out.

[JHow]

3. ...ordered 2 octal plugs that have diodes wired in them. I'm going to wait until the diode plugs arrive and try them first.

The plugs are cool. The "cheapskate/don't want to wait for shipper" solution is to just solder diodes on the socket pins.

4. The .01mf caps on the schematic numbered 12-15 I replaced with Sprague Orange Drops 600v 103J. The schematic lists polarity symbols for these caps, from what I understand these orange drop caps should work but aren't polarized. Should this be a concern? I do have other caps, some malory .01mf 600v but they aren't polarized either. I'm not sure caps of these values are made polarized and I don't know if it matters. Appreciate any advice and if I should get polarized caps for this, I'd grately appreciate referal to a source.

Polarized caps are not required in those places. your Spragues or mallorys will work great.

5. ...."16MF 450V" to a greater value in the 500V range.

I don't see more than 340VDC on the schemo. 450Volt is fine. If there is no price difference, 500V is good too.

[Jag]

Regarding the polarized capacitor you had installed backwards, any polarized capacitor that has been installed the wrong way around can be reasonably expected to fail. I would replace it with a new one.

52 Bill said, "Before you do anything else with the tubes and the rest of this amp, you need to find and fix the problem with the ac ground and the hot chassis"! So have many others! You NEED to address this issue first, stop randomly ordering and replacing parts. If you don't understand the many useful posts in this thread then you need to say so and ask for more direct pointers! You could continue ordering and replacing random parts until everything in the amp is new and then it might be fine (or not) but you won't really have fixed the problem or understand what it is/was.

[sig]

Final update.

I got the amp grounded and working today. I got tired of waiting for the diode plug and decided to try one of the NOS 5Y3s I received. Before I powered up, I went through everything once again. I found one resistor (#28 Phase Inverter Grid Resitor) that broke from a cold and / or old solder joint and I repaired that. Like I said before, I also corrected the polarity of the .005 cap (#16 on the schematic). The last thing I did was check for shorts from ground to AC from the power cord without tubes, next with 5Y3, next with 6L6s, next with 7F7s and all tubes, no shorts detected. I powered the amp up and she worked find and sounded very nice. I intend to go through it once more to check for any other loose ground connections and solder joints.

In closing, thank you everone for your patients and help. I realize I asked some dumb questions and I appoligize for that. Once I get the amp back in the cabinet and completed, I'll post a youtube video of her.

Regards everyone and Happy Holiday!

Paul

[JHow]

Glad it's working. I look forward to your picture. Does your example have the "musical staff and notation" theme as shown on the Photofact?

[Bruce / Mission Amps]

I have two of these exact same amps!... Buggers both of them.