20Segi tube amp

[noSmoking]

If you have the same values, no problem at all.
I guess you are talking about cathode bypass electrolytics.

so I can use them anywhere except power supply main caps?
I cleaned it up some more and Will start a tinycad schematic soon,I found a lot of loose wires and some REAL patch jobs,lol.
I got my tube tester out,I built it long ago,need to see if it still is working or if it gets repaired first,
I made some more Pictures after it was clean,doesn't look as old now!
I need to convert them so I will put them up in a few mins.
Thanks,
NS

 

[noSmoking]

Here's some picture of the cleaned up Segi20

 

[noSmoking]

here is the front and the tube tester

 

[noSmoking]

got one high rez up trying another

here is the front and the tube tester

That's the .1 caps

 

[noSmoking]

Checked my tube tester and something was rolling around inside,lol so out with the flathead screws,There it is a neon spare light bulb,
The tube tester works great and all my tubes are working also 6L6 are GE tested at 98%
The 12ax7 is a GE and tested at 85% 2 are 6201 USA with some green paint can't read thoses,and 1 NEC has 8 01 on it it tested at 87% so all the tubes seem ok! YEA!
I upload a pic
Thanks,
NS

 

[noSmoking]

I got some time to check out some components,the resistors,even the burnt green one checked good,The caps all checked bad some more than 30% off,so I will replace all of them,I am going to change some wires out for some different colors,cuts down on my confusion,lol.
The black box is indeed a choke,It's value was 2262 mh,I don't know if this is the correct value ,IS this value ok,or what should it be?
Thanks alot,
NS

 

[JMFahey]

The caps all checked bad some more than 30% off

Did they check BAD (as in shorted/leaky) or up to 30% off?
NOT the same thing.

That's not the way to troubleshoot an amp.

What is the actual problem you are trying to solve?
Which are the symptoms?

 

[noSmoking]

Hi JMFahey,
Original problem was no sound,one 6L6 got real bright,I decided to replace the parts not to specs and go from there,
I did check the caps with a sencore the Capacitance was off,ESR was ok and the leakage ran to zero,so I was replacing them due to incorrect reading uf,is this wrong?This amp was put together in 1977,so I thought after 10 years they dried out and change value? So almost 40 years on them,
The cap labeled 33uf checked at 67uf,the 2 100uf checked at 51 uf and 53uf ,
I am new at tubes I don't have experience at trouble shooting them ,but I am in here trying to learn !
Thanks for your help and patience with me,GOD loves idiots that's why he made so many,lol.
I have found alot of schematics but they are hard to read,looks like they were scanned,and no voltage readings on them,but I'll get it fixed just give me some time!
I see in the specs it says 400v unless specified,I have 16v 50v and others at 600v,should they all be 400v or better?
Thanks for your help,
NS

 

[noSmoking]

Hi All,
It's working ,I have some low static, sounds like white noise,it's just loud enough to hear,stays low with the volume up,where should I start to look for that one ,I have a scope and a dvm,
Thanks,
NS

 

[jjman]

Noise could be bad plate resistors or other things. Any hum from having the trannies lined up like that?

Very cool amp. The layout reminds me of Trainwrecks a little.

 

[doozerdave]

Hi All,
It's working ,I have some low static, sounds like white noise,it's just loud enough to hear,stays low with the volume up,where should I start to look for that one ,I have a scope and a dvm,
Thanks,
NS

Glad you got it up and running! 2.2H is a typical choke value. If the noise isn't increasing with volume then it's in the power amp. If it gets louder as you turn up the volume then it's in the pre-amp. I would replace all plate resistors if you haven't already. Hiss and low static could simply be a tube, maybe not a component, but old resistors are known to cause crackles when they're warm.

 

[noSmoking]

Hi jjman,

Noise could be bad plate resistors or other things. Any hum from having the trannies lined up like that?

Very cool amp. The layout reminds me of Trainwrecks a little.

I have some new resistors on the way, one of the resistors has been hot enough to burn the middle of the resistor,so it checked ok but don't look so good,I'll try the new one of see if it was the culprit,Thanks,
NO hum,I was surprised,I'm not a tube person yet,but most amp have the transformers apart as much as possible! but these are shielded,I don't know but the amp does sound good ,I have a electric bass a LTD nothing special but has modified pick up's Play's well!
I need to build a speaker cabinet for it ,I have the box for the head unit,I'm using a peavey 18" low rider in a ported sub box for now to test ,I got about 10 watts at half volume,I think it might put out 15 or 20 at max, ,lol.
The pot on the chasis how or where should it be adjusted to?
Thanks!
NS

 

[doozerdave]

The pot on the chasis how or where should it be adjusted to?
Thanks!
NS

That's likely the power tube bias adjust. You don't just set it, you need to make measurements to tweak it for balanced current in your output tubes.

Edit: Looking at the pictures again, I'm not sure what that pot is for. It appears to be connected between power supply and an input tube. How's your TinyCAD schematic coming along?

 

[noSmoking]

That's likely the power tube bias adjust. You don't just set it, you need to make measurements to tweak it for balanced current in your output tubes.

Edit: Looking at the pictures again, I'm not sure what that pot is for. It appears to be connected between power supply and an input tube. How's your TinyCAD schematic coming along?

Hi doozerdave,
I'm about ready to make the schematic,I have changed some wire colors and some other things to make it ez to comprehend,all the same wire color is crazy,lol. I think I got the hang of tinycad ,LOL,
I hate to be a nubie but how do I set the current on those tubes ,It looks like it's across the 6.3 on the 12ax7,
Thanks,
NS

 

[doozerdave]

Hi doozerdave,
I'm about ready to make the schematic,I have changed some wire colors and some other things to make it ez to comprehend,all the same wire color is crazy,lol. I think I got the hang of tinycad ,LOL,
I hate to be a nubie but how do I set the current on those tubes ,It looks like it's across the 6.3 on the 12ax7,
Thanks,
NS

Oh, maybe that is some sort of heater voltage balance pot for the 12's. Interesting.

I was asking about an updated schematic because I wanted to see if the 6L6's are cathode biased. If so, that explains why there is no pot for bias adjust.

 

[noSmoking]

well no hum,lol.

Noise could be bad plate resistors or other things. Any hum from having the trannies lined up like that?

Very cool amp. The layout reminds me of Trainwrecks a little.

Hi,
The plate resistor ,one has a burn mark on it so it's a part change for sure,might be the noise problem,I hope,also one cap in the tone controls is open,I got it on the way too.
I have downloaded some older files for tinycad off yahoo groups,if anyone that uses it,could point me to a good library it would be helpful,I have almost all of the parts filesto get started,mostly need to learn to make a library part,yahoo's are a little dated,but better than nothing!
I notice most tube amps have trannies on the opposite sides,but these are shielded,must be enough,lol.
I found some cement wire wounds,going to sub one in and see,new caps shipped today!
Thanks,
NS

 

[noSmoking]

Oh, maybe that is some sort of heater voltage balance pot for the 12's. Interesting.

I was asking about an updated schematic because I wanted to see if the 6L6's are cathode biased. If so, that explains why there is no pot for bias adjust.

Here's a pic of the bottom,not far enough along yet ,to know what your asking,

 

[noSmoking]

well I fixed the noise

Glad you got it up and running! 2.2H is a typical choke value. If the noise isn't increasing with volume then it's in the power amp. If it gets louder as you turn up the volume then it's in the pre-amp. I would replace all plate resistors if you haven't already. Hiss and low static could simply be a tube, maybe not a component, but old resistors are known to cause crackles when they're warm.

Hi,
The 1/4" Plug contacts were dirty inside the plastic box ,found it by accident,sat the guitar down and it went away,lol.a little contact spray and it's gone,lol.
The pot controls the heaters across 3 12ax7.I set it for 7 volts that seems to be a good place near where it was previously set,
The volume control knob wasn't at zero,so I checked all the knobs and now I ran it wide open my watts meter stops at 100 watts and it went passed that,nice signal there on the scope too,ez way to see if all the tone controls work looking at the output on a scope! I am pleased ,I'm going to have to find a use for 4 12ax7's and 2 6l6's now,lol.I think I found a ez schematic ,no tone controls ,but I don't need them,
I have some IRON that ran 4 6L6's and so it may do so again,lol.
I hope to start the schematic tomorrow as most of it 's in my head now,a fellow emailed me and told me TinyCad 2.80 is out and has a full library and a board layout tool,I goggled it showed right up,lol.
Thanks for the help,
NS

 

[doozerdave]

Yeah, can't really tell where those wires are going. The cathodes are tied together and then run off somewhere. The control grids have a resistor and then run off somewhere. Once you draw a proper schematic it will be obvious.

 

[noSmoking]

Hi,
Got my tubes in today but need a little help,
I ordered 6L6 and 12ax7.....Here's what I got
4 6n3c
1 6EW6
1 6AG5
1 6AT6
1 10DE7
1 6DT6A
1 6BN6
1 7AU7
1 6S4A
ALL tubes are NEW RCA and Philco,Paqna? on the 6L6.
So I have google some of these and they gave me a number I don't have ,so what do I have here,Or point me to where I need to go,Thanks,
NS