Webster 80 to 5C1 Champ Power Supply Questions

[jonathan_kea]

I am working on converting a Webster 80 wire recorder to a 5C1 champ as my first tube amp build.

1.) Based on the 6X5 Pin 3 & 5 voltage readings provided by the Webster 80 service manual, I have surmised that I have a 350-0-350 power transformer. Is that more voltage than would be typically found in a fender champ - will it overwhelm the circuit?

2.) As you can see from the Webster 80 schematic below, the original design had a 1k ohm speaker coil load in the power supply section. I've purchased a 20W 1K ohm resistor in the event that I need to place this between pin 8 of the 6X5 and the first filter cap on the 5C1 circuit, but I'm not sure it's needed. The 5C1 champ has a 500 ohm resistor between the first two filter caps - does that factor in to the application of the 20W 1K ohm field coil resistor replacement in any way? Do I even need the 20W 1K ohm resistor?

Thank you!

[sluckey]

I need to place this (1K 20W resistor) between pin 8 of the 6X5 and the first filter cap on the 5C1

Do this and you'll be fine.

[jonathan_kea]

Another question: I want to have just a single input on my build. Any considerations when doing this? Each input currently leads into a 75k resistor. Can I simply eliminate one input jack and it’s 75k resistor and call it a day?

[sluckey]

Another question: I want to have just a single input on my build. Any considerations when doing this? Each input currently leads into a 75k resistor. Can I simply eliminate one input jack and it’s 75k resistor and call it a day?

yes

[ac427v]

I've never looked at a Webster schematic before. The power supply filtering is amazing! The first node has a 25u cap, 1000 ohm choke (or resistor) and a 15u cap. The Champ had much less filtering but the hum was nearly inaudible because of the limited low frequency response of the output transformer and small speaker. If your OT and speaker are better quality you may hear too much hum with the Champ circuit. If you're still at the parts-ordering-stage you could get an extra 16u/450v cap to allow emulation of the Webster power supply if needed.

[jonathan_kea]

Interesting! Thanks for the tip. The original speaker was blown, and had the 1k ohm resistor in the voice coil. I have replaced it with a big 20w 1k ohm resistor in the new build.

I've decided to draw a point to point wiring diagram for this project in DIYLC as the off the shelf Champ turret board i bought did not fill well with the existing chassis and layout. I will post the DIYLC layout when I'm done to see what you guys think.

Another question for the hive: The original output transformer secondary leads are faded and appear to be the same color. Is there any way to determine which secondary lead is the COMMON using a volt meter?

Appreciate everyone's help!

[sluckey]

Another question for the hive: The original output transformer secondary leads are faded and appear to be the same color. Is there any way to determine which secondary lead is the COMMON using a volt meter?

Doesn't matter. Close your eyes and pick one.

[2deaf]

Another question for the hive: The original output transformer secondary leads are faded and appear to be the same color. Is there any way to determine which secondary lead is the COMMON using a volt meter?

Do you mean only the two RED leads or all of the secondary leads?

The heater leads and their center tap will have a very low resistance between them and you may not be able to determine which lead is the center tap with a multimeter reading resistance.

The high voltage leads will have much higher resistance.  The resistance between RED and RED will be the highest resistance.  The resistance from either RED to the center tap will be approximately half the resistance from RED to RED. 

[PRR]

The question seems to be about the "output transformer".

[2deaf]

The question seems to be about the "output transformer".

Oh.  Never mind, then.

[jonathan_kea]

Would you guys take a look at the DIYLC point-to-point layout diagram for my Webster 80 to 5C1 conversion? Components are placed as they are because I am working with the topology of the original amp (see placement of tone control + on/off, for example).

Full disclosure, I am a complete novice and this is my first project, so please let me know if you see anything out of place or missing - I really appreciate everyone's help and advice.

[2deaf]

Pins 1 and 3 need to be grounded on the 6SJ7. And 5.

Yellow wire to 6V6 pin 5 doesn't quite touch the pin.

[sluckey]

I recommend connecting a 22µF cap directly to pin 8 of the rectifier tube for better filtering/less hum.

I would also move the speaker jack far away from the tone control.

[PRR]

There no CT on the PT HV winding??

And you want center reference on the heater winding.

[jonathan_kea]

Correct there is no center tap on the HC winding or the heaters. I have seen how people install the two resistors on the pilot lamp. I will update the drawing to include those.

sluckey: Would the 22uf go in series between pin 8 and the 20W resistor? (20W resistor replaces voice coil from original speaker...) I assume you are not recommending an an electrolytic capacitor?

[sluckey]

there is no center tap on the HC winding or the heaters. I have seen how people install the two resistors on the pilot lamp.

Well there must be a HT center tap for that rectifier to work. The schematic shows a center tap for the HT winding and the filament winding. It's possible that those two centertaps are internally connected to the transformer frame. Lot's of cheap electronics did that. Measure the resistance from each HT lead and each filament lead to the transformer frame to determine if these center taps are indeed internally connected. Otherwise, look for the missing center tap wires.

sluckey: Would the 22uf go in series between pin 8 and the 20W resistor?

No. Connect the positive lead to the tube socket. Connect the negative lead to chassis.

[jonathan_kea]

There are definitely only 4 leads coming out of the PT secondary side... The HT resistance readings were ~181ohms and ~195ohms respectively. The heaters measured in at .4 ohms (exactly) each. Do those readings sound reasonable?

[2deaf]

There are definitely only 4 leads coming out of the PT secondary side... The HT resistance readings were ~181ohms and ~195ohms respectively. The heaters measured in at .4 ohms (exactly) each. Do those readings sound reasonable?

Hey, now my reply #7 makes a little bit of sense. 

[sluckey]

There are definitely only 4 leads coming out of the PT secondary side... The HT resistance readings were ~181ohms and ~195ohms respectively. The heaters measured in at .4 ohms (exactly) each. Do those readings sound reasonable?

Very reasonable and confirms the center taps are internally connected to the frame (ground). You don't need to add resistors to the pilot lamp.

[jonathan_kea]

Thanks! Would you guys be able to tell me if the resistors and caps coming off the 6SJ7 look correct in terms of assembly? I believe i transposed them correctly from the Weber 5C1 layout but its hard to think in three dimensions sometimes - a 2nd set of eyes would be appreciated!

[shooter]

Pins 1 and 3 need to be grounded on the 6SJ7. And 5.

I followed pins to parts, they match up, didn't follow parts

[ac427v]

I connect the house power HOT (black) wire to the fuse tip, fuse side terminal to the power switch, power switch to PT primary wire.
I connect the house power NEUTRAL (white) wire to the other PT primary wire.

[jonathan_kea]

Thanks ya'll! Also wanted to let you know that the original chassis has the tone and power switch right beside the output jack, but used a shielded wire. I really don't like having to set the tone every time I turn on the amp, but would like to keep the original setup because it matches the labeling on the cover plate. If it's problematic I may move the jack. The original wire recorder was surprisingly quiet considered it was designed in the 40's. I hope to start wiring it up in the next few days. I really appreciate everyone's comments. Will post some pics when done.

[jonathan_kea]

Last question! Would it be better to ground the 6v6 cathode resistor/capacitor to the same point as the power supply caps, the lug on the 6SJ7 tube socket, or kind of floating in the middle as drawn? The chassis is 100% copper plated similar to the original 5C1's, by the way...

[sluckey]

I suggest the filter caps ground.

[jonathan_kea]

In the power supply of the Weber 5C1 champ layout, it shows a 500 ohm resistor and a 25k resistor between the filter caps. Do both of these resistors need to be 2W? I have a 2W 500 ohm resistor on hand, but only a 1/2W 25k ohm resistor.

In Mojotone's 5F1 champ layout, they use a 2W 10k resistor between the 16uf and 8uf caps and a 22k 1/2W resistor between the two 8uf caps, hence the question.

[shooter]

If I did the math correct (sqr root(.5/25000)) ~~ 4.4mA
so that's your limiting factor
if you got 2 47k 1/2W in parallel might be a better option 

[2deaf]

In the power supply of the Weber 5C1 champ layout, it shows a 500 ohm resistor and a 25k resistor between the filter caps. Do both of these resistors need to be 2W? I have a 2W 500 ohm resistor on hand, but only a 1/2W 25k ohm resistor.

In Mojotone's 5F1 champ layout, they use a 2W 10k resistor between the 16uf and 8uf caps and a 22k 1/2W resistor between the two 8uf caps, hence the question.

Fender shows the 6SJ7 drawing less than 1mA.  1mA through 25K = 25V.   25V x .001A = .025W   A 1/2W resistor will be fine.

[jonathan_kea]

Shopping online for these resistors (500 & 25K) and there appear to only be 470 & 510 and 22K and 27K available - do you pick the closest value, or is it better to go slightly higher or lower?

[sluckey]

https://www.tubesandmore.com/products/resistors-5-watt-wirewound-power

[jonathan_kea]

The layout calls for 2W and 1/2W resistors in between the caps - not sure I could fit that big 5W on the terminal strip I am working with.

[shooter]

you pick the closest value

If you're trying to get to the 3rd decimal point, spend more money, otherwise play guitar with loose tolerance 

[jonathan_kea]

Perfect - thank you!

[jonathan_kea]

I finally finished all the wiring this afternoon, fired up the amp, and nothing....!

The pilot light is lit and all the tubes are lit and warming up reasonably.

The speaker is vibrating steadily/constantly and every once in a while a little fizz or pop squeezes through, but otherwise it is dead quiet. My first thought is that the 6SJ7 is bad.

Any other ideas as to where to start with this? Anybody know what a vibrating speaker w/no sound could mean?  I checked the resistance across the speaker cord and it was 4.6 ohms as expected...seems good.

[shooter]

PS voltages?
tube voltages?

without power verify NO shorts at input jack

[jonathan_kea]

Apologies for the newbie question, but how would you verify there are no shorts to the jack? Open between tip and sleeve or ...?

[jonathan_kea]

Running a voltmeter from the tip of my input cord, I am getting 67k ohms past the first resistor that goes to pin 4 of the 6sj7. All good there.

When I run from tip to the other side of the .022 to pin 4 I got OL on the voltmeter... replaced the cap and got OL again.

I checked a random cap in my box and got a continuity measurement. Is it possible that I have fried the .022 cap twice? I was pretty dainty with it the 2nd time. And I’m getting an accurate capacitance reading across both legs of the cap that has been soldered in... what gives?

I’m going to take a break and get some voltages tomorrow.

[jonathan_kea]

Hello All,

Here are the voltages I took this evening from the 5C1 build. Do these look OK?

6X5
PIN 2:   2.5 VAC
PIN 3: 304.7 VAC
PIN 4:
PIN 5: 305.6 VAC
PIN 6:
PIN 7:   2.9 VAC
PIN 8: 270.0 VDC

6V6S
PIN 2:   2.9 VAC
PIN 3: 169.0 VDC
PIN 4: 194.8 VDC
PIN 5:   3.5 VDC
PIN 6:
PIN 7:   2.9 VAC
PIN 8:  31.7 VDC

6SJ7
PIN 2:   2.9 VAC
PIN 3:
PIN 4: -1.29 VDC
PIN 5:
PIN 6: 17.13 VDC
PIN 7:   2.9 VAC
PIN 8: 101.6 VDC

1st Filter Cap (16uf): 202.5 VDC
2nd Filter Cap (8uf):  197.2 VDC
3rd FIlter Cap (8uf):  186.3 VDC

[Ed_Chambley]

https://ampgarage.com/forum/viewtopic.php?t=30019


Check the link. Great discussion on seting the 6sj7 and a long thread with testing very good.


I also use a 6sk7, pentode and is a tv tube, but the amp doesnt know.

[jonathan_kea]

Hello All,

Having trouble uploading photos, but wanted to provide the following update:

MAJOR FIREWORKS!!!

I started the amp up this afternoon to do some additional testing - after powering up the unit, I turned up the volume knob and got arcs going from the potentiometer case to to the ground buss. When I measure the resistance across the sleeve and tip of a guitar cord plugged into the input jack I get 'OL,' which I assume means I have an open circuit somehow?

See attached photo of the potentiometers, jacks, and ground buss. (ground buss runs from input jack to output jack to create a ground for potentiometers and shielded signal wires, will attempt to upload a photo later...)

PS - I also think that the voltages I posted earlier are way off compared to what others have posted for 5C1 voltages....  odd that it arced today, since I had it up and running for at least an hour last night without arcing, funny smells, etc.

Thoughts?