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 Post subject: tweed rectifier voltages
PostPosted: Fri Jan 08, 2016 6:38 pm 
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Hello folks.
Finished Tweed build. Passed the no smoke test. Now doing the voltage checks. All is not well. Rectifier 4 & 6 are at 360. Yay. Rectifier pin 2 is 5.57. Rectifier pin 8 is basically zero. I have 3.1 volts on 2 & 7 of V3 and V4 and 3.1 volts on 4/5 and 9 of V1 and V2. So I'm missing half the juice. I reflowed the solder on 8 which looked fine to begin with. The pin seems fine as there is continuity between the inside and outside portions of the pin. I saw another post that referred to this issue so I checked the green leads on the indicator...they read 6.2. Any wisdom would be greatly appreciated.
George


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PostPosted: Fri Jan 08, 2016 11:41 pm 
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3.1 each side to ground = 6.2 VAC ? is this what you have?

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PostPosted: Fri Jan 08, 2016 11:48 pm 
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3.1 volts AC from the tube heater pins to ground is normal. The center tap of the heater winding on the power transformer is grounded so the heater voltage is balanced with respect to ground. If you measure across pins 2 and 7 of V3 or V4 you should read 6.3 volts AC. Same with measuring across pins 4/5 and 9 of V1 and V2. Same with measuring across the pilot light which you have done and got a good reading.

You should read about 5 volts AC across pins 8 and 2 of the rectifier.

At pin 8 you should get a DC reading. It's pulsating DC if the standby switch is open. That's because none of the filter capacitors are in circuit. It won't read 370, but it should still be fairly high.

With all the tubes in place and the standby switched closed you should get around 370 volts DC at pin 8 of the rectifier. If only the rectifier tube is in place and the standby switched closed you should get a DC reading higher than 370 because there is no load.


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PostPosted: Sat Jan 09, 2016 1:01 am 
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OK, thanks Stephen and Mitch, very helpful as usual. I am in fact getting the 6.3 values when I measure "across" the appropriate pins. I was interpreting the instructions as measuring each pin relative to ground. Yes, rookie, non-electronics awareness. Now, at pin 8 on the rectifier socket I get -27.8 with the standby switch in the "up" position and .850 with the toggle in the down (as in towards where it says "standby" on the face). As you can tell, I don't fully understand how the standby works. On my Deluxe Reverb, when toggle is towards "Standby" there is no power to speakers, toggled away from standby, sounds are made. On my Tweed, with the toggle towards "Standby" there is continuity between the pins. Wiring appears correct. Apologies for the naive questions. And thanks much for the support.


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PostPosted: Sat Jan 09, 2016 4:25 am 
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How the rectifier works: The voltage of the power transformer high-voltage secondary is applied to the plates of the 5Y3 rectifier tube. This tube has a directly heated cathode (the cathode and filament are the same element), so the pulsating DC is taken off of pin 8, which is one side of the filament. The plates act as a one-way gate to allow current to flow only when the plate is positive with respect to the cathode. Because the high-voltage winding center tap is grounded and is the zero reference point, each plate is positive only on one-half of the AC cycle. During one-half of the cycle, plate #1 will be positive with respect to the cathode, and during the second half of the AC cycle, plate #2 will be positive with respect to the cathode. This causes the voltage on the cathode of the rectifier to be a pulsating DC voltage.

You also need to measure the DC after the standby switch to see if that is working correctly.

check out this article for some good information on the 5E3 circuit https://robrobinette.com/How_The_5E3_Deluxe_Works.htm

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PostPosted: Sun Jan 10, 2016 7:25 pm 
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Thanks for your reply and for that great link. Very helpful. Getting closer to the holy grail...closer. First, my voltages:
V4 and V3 basically identical: 3-363, 4-326, 8-20.6;
V1 (12ay7): 1-127, 3-1.87, 6-129, 8-1.86
V2 (12ax7): 1-159, 3-1.21, 6-198, 7-9.8, 8-43.3

I think this is all ok.

******Before you read the next section, you can jump to the end and see that I seem to have found my problem but I'm not certain and I still need a solution. If you want to read about strange things that happen when one puts resistors in the wrong place, by all means be my guest.


Bright channel is quiet and plays beautifully on both hi and lo inputs. I have hope!

Normal channel has a pronounced hum without an instrument plugged in. Adds a significant hum when turned up while plugged into bright channel. When plugged into normal channel, on Hi input, significant buzz and some nasty raspy noises at moderately high volume. No rasp in the Lo input. Poking around with a plastic implement, yellow wire on pin 7 or V1 is microphonic, as are the yellow leads coming from the 68k resistor pairs. Grounds all seem to be ok for continuity. Before I start remelting things, some wise input would be much appreciated.

******Hold everything. I think I see the issue. I've put the 1M resistors on the LO inputs. I'm guessing fixing this might fix my problem but I'm not certain. If so, is there an easy way to reroute wiring without moving the resistors so that I don't have to try and get into the inputs?

Thanks in advance for your help.


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PostPosted: Mon Jan 11, 2016 2:10 am 
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You probably have found the problem. No easy way to fix it though. Move the resistors so the input jack wiring is proper. The input circuitry won't work right if the 1M's aren't in the right place.

The 5E3 article by Rob Robinette that Stephen mentioned is an excellent description of how the amp works. He has another article on the same site about how the Fender input jacks work. If you read it you will see that putting the 1M's in the wrong place will upset everything.
https://robrobinette.com/How_Fender_Inp ... s_Work.htm

Your voltages are all good. The amp should work properly if you fix the input jack wiring. Make sure all your grounds are good, too.


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PostPosted: Mon Jan 11, 2016 8:49 am 
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This has never happend to me so I'd like to hear how it turns out after you make the change.

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PostPosted: Mon Jan 11, 2016 8:30 pm 
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Hello fellow Tweeders and other interested parties.


The very good news is that my Tweed rules! Pulled out the inputs and rewired them appropriately (my spatial relations abilities are not strong so I wasn't "seeing" the orientation of the inputs correctly). It is loud, sparkly, grungy. Neil comes through loud and clear, as does Hotel California. And the cleans are also quite good and hold for plenty of decibels. The amp is MUCH quieter than my Fender Pro Junior, I dare say quitter than Deluxe Reverb. Guess who's got some amps for sale!?

You were both right about that crazy input wiring. Strange things happened...none of them good. Just a good thing that my error wasn't in a "blow everything up" part of the amp. I've attached a picture of the finished product. Not "Olivia" quality, I must admit. I've taken lots of pictures of stages along the way. If anyone's interested, let me know. The pictures I found in the forum and sent to me by forum members were very helpful. The colour really helps.

I'm going to get some weatherstripping before I batten everything down. I had lots of vibration issues with my Champ build so I'd like to try and prevent that if possible.

Thanks to all who responded to my novice and electrically naive questions. I'm by no means an expert now but I can say I know considerable more than when I started.

Cheers,

George


Attachments:
Inputs Working.JPG
Inputs Working.JPG [ 3.93 MiB | Viewed 7908 times ]
Tweed Done.JPG
Tweed Done.JPG [ 2.66 MiB | Viewed 7908 times ]
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PostPosted: Mon Jan 11, 2016 10:13 pm 
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Glad to hear your amp is working! It's good that you found the trouble and fixed it, too. That's extra added experience you wouldn't get if it worked the first time.

Your pictures look good. Having it work reliably and sounding great is the important thing. We can all learn a thing or two from Olivia, though. Even I had to go back and rewire a couple of things in my Tweed after seeing her pictures, and I've been building electronic projects for over 40 years.

Happy playing!


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PostPosted: Tue Jan 12, 2016 11:19 am 
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Ha, Olivia rules!!

There are two threaded holes in the rear flanges. These are for 4-40 screws to batten down the rear panel if you find it necessary. BTW, If you want more headroom, check out the tweaks in the manual.

Build looks pretty clean, good job!!

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