Increasing Filter cap values

[pbman1953]

Keep in mind that I  did the measurements with the cap feed-green  wire off. I took both measurements from that point.

[sluckey]

Well then, those voltage readings don't mean very much. Guess you don't know how it sounds yet. Keep us posted.

[pbman1953]

Since you to told  me to disconnect the cap feed, I was afraid of reconnecting until told to.


I can give it a go .

[PRR]

> wasn't sure if they were overkill

"No such thing" as overkill when specifying an amp this big.

The normal PIV for the apparent 400V AC and some assumptions is 1,130V. Three 1,000V diodes series is just enough overkill.

The startup first-cycle current is 24 Amps!!  Once started, 3.3A peak and 0.83A RMS. The 1A diodes are right near the edge of death.

> 1N5408s that are rated 1000v/3A. Less than 40 cents each.

Agreed. Buy six; you need at least two-series in each leg to stand the PIV, and I've learned to use more-than-double PIV to survive line spikes. 1,130*2= 2,260V needed, so three 1,000V parts each leg.

I would not worry about PT damage. It takes time to heat large copper. The peak current comes way down real quick, pretty OK by the second cycle.

Ah-- the real danger to PT is when marginal diodes short-out. "Overkilling" from 30-cent to 40-cent (or even $10 retail) diodes may save a $200 PT from smoke-death.

[pbman1953]

PRR




In that case , should I not try it with the diodes  I have installed?

[Ed_Chambley]

I am not PRR, but I would try it. You might lose a Diode, but I doubt it. It would probably take a while to kill them.


You need to build a light Bulb current limiter. You can search the forum, do a Google search or best of all, search for a link to Sluckey amp scrapbook. It has instructions to make one and other things you should read.


Did you do anything that could have killed the diodes like hooking up wrong initially? We need to find the cause of the Diode failure. Could be over stressed.


Easy to make a mistake with diodes and they pop easily if current hits them the wrong way.

[Ed_Chambley]

I am concerned you may be getting confused with the series caps.

[pbman1953]

Ok, partial success.


I turn amp on , no fuses blowing.


I threw the stand by and there's a hum , low volume and one tube red plating.


I know that's not good.

[Ed_Chambley]

I cannot see for sure, it looks as if you have from the diodes a green wire that is your B+ and it probably goes to a switch. From the switch you have a blue wire then a resistor then a red wire and a resistor then a black wire going to ground. If this is correct you have grounded your B+.


From the first series cap, which appears to be the one with the red wire on the negative side of the cap. From the positive side of this cap is where your next B+ connection is made. Yes it will still be grounded, but your current will have somewhere to go.


If this is how you have it, do not power up the amp.

[Ed_Chambley]

You have something miswired. Check and insure my previous post.

[Ed_Chambley]

I am betting that you have no connection from your first series caps to the screen node.

[pbman1953]

The green wire is the cap feed-


Also attaches to-


15k/5x(r31),  input to the Classic Tone chock (r42) & Blue wire to new C27 A&B


The return from the Classic tone goes to the C28 A&B & the 1k 25w (R30)




The blue wire off the standby is the new filament transformer (green)




The red wire off the switch is really the red/yellow from the PT


The resistors you see were a mode, I think you suggested and then not to use the PT- green / yellow wire.

[Ed_Chambley]

Do you have a variac? Any way to reduce your ac voltage. I do not know if you pull your tubes if your unloaded voltages will kill the caps.


Anyway, what I am getting at is being able to check voltages. Sit tight and maybe one of the guys who knows for sure will let us both know. I do not want you to kill the new caps.


Checking volts will let us know, but red plating is a sign. Anyway I can assure you it is not wired right and I can't see for sure because of the wire splicing. I cannot follow the path.


Build a bulb limiter ASAP!


I am still looking at the photos, but I am not sure.

[sluckey]

I can't tell how it's wired from the photos either.

[Ed_Chambley]

Rich the wire going to the 550 350 caps is yellow and spliced, correct.?


If so, where it connects you should have a wire from it connected to the next node. Where does it connect? It looks like it just goes through the caps to ground. It needs to connect to the next node.


Tell us where this wire continues to?

[pbman1953]

That yellow wire is only extended to reach the caps.


It goes from the 550's to the 1K25W res & other side of r42 (classic tone choke)

[pbman1953]

I  tried a test to see if that plating tube was bad so I moved it to a different socket.


The same socket glowed so I guess the tube is ok.


Still with the same issue

[DummyLoad]

pull all the power tubes. measure dc voltage at pin 5 on all 4 power tube sockets. make sure they all read the same. use a octal socket base on the suspect socket to make sure the socket pins are making contact with the tube base pins.

octal base - https://www.tubedepot.com/products/8-pin-octal-tube-base-only

--pete

[pbman1953]

Good point.


I can do all this later and report back.   I'll check the #5 and then I'll flip the amp over and see if all the pin sleeves are in a correct position. Possibly tighten them too.






Thanks

[sluckey]

Will you be playing bass through this amp?

[pbman1953]

Yes, only bass.

[pbman1953]

Measurments-




From diodes/ C27 A&B-   575 volts


C28 A&B-   574




tube 1- term#5-  -102 in stand by,   -064 On


Tube 2(red plater) - +70 in stand by, + 274, when on


Tube 3  & 4 - similar to tube #1


C29-    +092 in SB, +370 when on


C32-  +139 in SB,  +283 when on

[sluckey]

Tube 2(red plater) - +70 in stand by, + 274, when on

Gotta fix this.

[pbman1953]

Sorry to say but have to be honest, that I had the #5 pin, on the plating tube,  hooked to the preamp feed line.Same as C32, Hence getting 274 volts. I found the right connection at where the line comes from the bias pot.


no hum, super quiet. No time now to button up. Will have to clean up a little, re bias and get the 3 amp diodes.


You guys are the best , thanks.

[pbman1953]

If I have a 3.3 k for R51 & 52 do I need r26 & 27?

[shooter]

probably not as long as you wire it correctly.  I personally like to solder the grid R's right at the socket so I would probably use 4.

[pbman1953]

R51 & 52 are on the board


26 & 27 were wired at the #5 pin

[sluckey]

If I have a 3.3 k for R51 & 52 do I need r26 & 27?

Yes. You need all 4 of those resistors.

[DummyLoad]

if it were mine, i'd change R51 R52 R27 R26 to 10K 1/2watt carbon comp. resistors and locate them at the socket if possible.


--pete

[pbman1953]

Hmm if thats the case try to following me here. Please go to reply 45 and look at the middle picture.




Keep in mind that Ed suggested a while back to change R24 & 25 to 100 k and R's 51 & 52 to 3.3k.


There are 4 -#5 pin wires.


Tubes starting from the left:
The #5 wire is direct to the board - w/ 3.3k to 100K then to bias feed- This is how the amp came with no 1.5k attached


Second tube- From pin 5 with a 1.5K shrink under the wire- Black shrink to Green cloth, to r25 & 51 joint


Third-  from pin 5 with a 1.5K shrink under the wire- Black shrink to red cloth to R  52 & 24 joint


Fourth-  From pin 5, green cloth wire to r52 & 27 joint with no 1.5k resistor.


The point I 'm trying to make is the out side tubes do not have the 1.5k resistor and insides do.

[sluckey]

The point I 'm trying to make is the out side tubes do not have the 1.5k resistor and insides do.

The point I'm trying to make is... wire it like the schematic. Those Traynor folks were probably a lot more savy than me.

[pbman1953]

Ok, I'll do that.


Thanks

[PRR]

Did the amp ever work?

If so, why are you adding/subtracting/changing resistors?

I thought the project was Big Caps. Don't complicate it by changing other things until the ONE big change is proved.

[pbman1953]

Yes it did work. All I wanted was a cap upgrade. But I noticed parts that were missing compared to the schematic.

[pbman1953]

Here's what I have found as far as connections compared to the schematic. Please keep in mind when I originally started to update parts with what I saw and replaced part for part. Now, with the help of the forum I've learned to use the schematic more.


So that being said I've noticed a weird thing.


C18-  is connected at the joint of R25 & 51 , the other side goes to lower connection (on schematic) of R23




C19-  is connected at the joint of R24 & 52 , the other side goes to upper  connection (on schematic) of R22

Since the routing was not the same as on paper , what's the effect?

Thanks

[sluckey]

C18-  is connected at the joint of R25 & 51 , the other side goes to lower connection (on schematic) of R23

C19-  is connected at the joint of R24 & 52 , the other side goes to upper  connection (on schematic) of R22

Again, that's not right. Make it like the schematic!

What's the effect? V4 and V6 have no grid stoppers. V5 and V6 have two grid stoppers 1.5K + 1.5K = 3K.

Wire it according to the schematic.

[pbman1953]

ok, I'll do that. Again, I've made some errors but won't take credit for this one. 

[Ed_Chambley]

Hmm if thats the case try to following me here. Please go to reply 45 and look at the middle picture.




Keep in mind that Ed suggested a while back to change R24 & 25 to 100 k and R's 51 & 52 to 3.3k.


There are 4 -#5 pin wires.


Tubes starting from the left:
The #5 wire is direct to the board - w/ 3.3k to 100K then to bias feed- This is how the amp came with no 1.5k attached


Second tube- From pin 5 with a 1.5K shrink under the wire- Black shrink to Green cloth, to r25 & 51 joint


Third-  from pin 5 with a 1.5K shrink under the wire- Black shrink to red cloth to R  52 & 24 joint


Fourth-  From pin 5, green cloth wire to r52 & 27 joint with no 1.5k resistor.


The point I 'm trying to make is the out side tubes do not have the 1.5k resistor and insides do.

Little explanation as to the resistor changes.

Referring to the change in grid leak size when using the KT120 tubes reducing the grid leak is a balancing act. The grid is in relatively close proximity to the (heated) cathode, therefore the grid has a tendency to warm up a bit itself, and can emit a few electrons. This would otherwise cause the grid to become charged, were it not for the grid leak, which allows these electrons to be replenished from the ground return, thus keeping the grid at the desired grid-to-cathode voltage. More powerful tubes have a higher propensity for the grid to warm up, so you want a smaller grid leak resistance (all other things being equal) to ensure the grid remains at its desired potential.

The recommended change of those resistors is a result of me burning up a quad in 2 Dyanco amps.  The 100K was recommended from New Sensor for *most* circuits.  I had a super lead Marshall running them with 150K grid leaks and even had to reduce these some.  His first set of tubes got very noisy and he has to replace them.

Also a couple of changes in V1 were done to add more warmth and the 3.3K replacing the 1.5K seems to smooth out the attack some in a Bass amp.  At least it does to me.

I write this so you guys who are helping him know why the resistors were changed.  None of these things should have been done while the change in cap values and the amp was running fine, however I did not know 2 sockets were missing grid stoppers.

Please correct anything I may have steered Rich wrongly with.  This does not include lead dress.  I had nothing to do with this.

[pbman1953]

C18-  is connected at the joint of R25 & 51 , the other side goes to lower connection (on schematic) of R23

C19-  is connected at the joint of R24 & 52 , the other side goes to upper  connection (on schematic) of R22

Again, that's not right. Make it like the schematic!

What's the effect? V4 and V6 have no grid stoppers. V5 and V6 have two grid stoppers 1.5K + 1.5K = 3K.

Wire it according to the schematic.

Also, what's the adverse effect of the caps (18 &19 ) not wired right?

[sluckey]

Also, what's the adverse effect of the caps (18 &19 ) not wired right?
Modify message

That depends on ***HOW*** they are miswired. I looked closely at your hi-rez pic of the board in that area and I saw several bad mistakes. I bet if I had my hands on the amp I could find more. Someone with poor soldering skills has been all over that area of the board. I suspect their electronics skills match their soldering skills.

It's not important to know who boogered this amp but it's up to you to make it right. I've been harping "make it like the schematic". I don't know that we can untangle it for you over the net. If you can't make it like the schematic you should take it to someone who can.

[pbman1953]

Sadly , I know it's not very pretty so I'll see what I can do to try and do some house cleaning.




Totally appreciate you and all the members for getting me on the right track.

[pbman1953]

I'm in much better shape. I got the parts to make sure all pin 5's had 1.5k resistors.


I did have a casualty in that red plated tube may be dead. It measures half the ma current compared to the others and all 4 sockets have the same measurements at their pins.


I moved the bad tube around and the issue moved with the tube.


Looks like I need one tube.


Also from a quick test out the amp is stlil very quiet and punchy.

[SoundmasterG]

Often when you have a tube red plating, and you are working on the amp and trying to troubleshoot without fixing the issue causing the red plating immediately, then that tube will be irreversibly damaged. The bias on that tube will be way off from the others and it won't have a stable bias and will drift and eventually red plate again. Sometimes the other one in the pair can also be damaged. Red plating is something you want as little of as possible, and you want to fix as soon as possible, preferably without running the tubes in circuit while you are troubleshooting. You also should make sure the socket didn't arc as it will make any tube put into that socket malfunction if the socket has arced.


Greg

[pbman1953]

Thanks Greg.


I played the amp tonight and sounded real good. Even with one bad tube. I ordered a new one. I'll write back after I get it.

[pbman1953]

Just a further update on the amp and it's doing well!


I was talking to Ed about tweaking some of the characteristics to the sound and he told me to install 4 - 3.9k resistors to all 4 pin 5's . I do have 4- 4.7k and I'm wondering if that's too high a value. Otherwise I'll have to get the closest I can to 3.9k. Most likely the store will have 4k.

[DummyLoad]

3.9k is a standard value.


--pete

[pbman1953]

Thanks for that, Pete, but to save a trip , is the 4.7 too high a value for that usage?


I've seen some Marshall, which Ed said the amp is based on, with 5...k

[DummyLoad]

they'll work. marshall uses 10k in that position.


--pete

[pbman1953]

I tried the 4.7's and there was an improvement. Thanks