trinityamps.com

Trinity Amps Guitar Amp Forum
It is currently Mon Jul 06, 2020 1:32 pm

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 21 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: Voltages - too low?
PostPosted: Sun Feb 16, 2020 8:41 pm 
Offline

Joined: Thu Nov 21, 2019 8:14 pm
Posts: 9
Location: Kanata, Ontario
Hello,

Finished building the OSD kit ... my first amp kit. All controls work as expected and it sounds super.

The voltages are lower than shown in the Builder's Guide. Are they too low or within the expected range ?

With 6V6's biased at 19 & 21.5
B+1 - B+5: 416, 408, 400, 277, 269

V1: 178 - 1.36 - - 170 - 1.5
V2: 184 - 1.38 - - 175 - 1.5
V3: 281 32 54 - - 288 33 54

V4: - - 408 407 - - - -
V5: - - 409 408 - - - -

Power Trans: 325 & 325 VDC (with tubes)
Line voltage: 120 VAC

All tubes are Mesa (in case that makes a difference).

Without tubes, B+1 - B+5: 448, 445, 443, 383, 377

- GK


Top
 Profile  
 
 Post subject: Re: Voltages - too low?
PostPosted: Mon Feb 17, 2020 11:14 pm 
Offline
Experienced
Experienced

Joined: Wed Sep 12, 2018 5:17 pm
Posts: 316
Location: Shawnee, OK
George, with tube amps, usually within +/- 10% is considered good. They seem low, just looking at voltage chart. Were you unable to bias the 6V6's at the recommended 22mA? Posting a good clear picture of the amp guts might help the gurus diagnose the problem, also. If no one else replies, PM (Personal Message) Coco (Stephen) or one of the moderators using the User Control Panel on main page (top right of page). Could be bad solder joints. Sorry I can't offer much help, haven't built an OSD yet.

_________________
"The only problem with being retired is you never get a day off"


Top
 Profile  
 
 Post subject: Re: Voltages - too low?
PostPosted: Mon Feb 17, 2020 11:18 pm 
Offline
Experienced
Experienced

Joined: Wed Sep 12, 2018 5:17 pm
Posts: 316
Location: Shawnee, OK
You can also click on Coco in the Moderator line, too.

_________________
"The only problem with being retired is you never get a day off"


Top
 Profile  
 
 Post subject: Re: Voltages - too low?
PostPosted: Tue Feb 18, 2020 11:28 pm 
Offline

Joined: Thu Nov 21, 2019 8:14 pm
Posts: 9
Location: Kanata, Ontario
Thank you Hankules.

I checked resistance among all of the leads & wires at B+1. And I did the same for B+2 through B+5. Most are at 0.0 ohms, with only 1 or 2 at .1 ohms.

I even re-heated the eyelets and ensured good contact among leads at B+3 through B+5. No changes in voltages.

And attached are some photos.


Attachments:
DSCN1678.JPG
DSCN1678.JPG [ 3.03 MiB | Viewed 931 times ]
DSCN1679.JPG
DSCN1679.JPG [ 3.04 MiB | Viewed 931 times ]
DSCN1671.JPG
DSCN1671.JPG [ 3.2 MiB | Viewed 931 times ]
Top
 Profile  
 
 Post subject: Re: Voltages - too low?
PostPosted: Tue Feb 18, 2020 11:39 pm 
Offline
Holy Ghost
Holy Ghost
User avatar

Joined: Sun Mar 13, 2005 4:10 pm
Posts: 7428
Location: Brighton, Canada
Congrats for getting so far!!

They are low and it would be ideal if you could increase them. Can you confirm that you used the 120V connections and not 110 by accident. That would make a 10% difference.
I would like to know what the AC voltages are, no tubes installed (i.e. no load) .
Presumably when you back off on the bias, the DC voltages rise.
I just built an OSD and voltages were bang on so yours should be as well.

All that said, if you like it, it is good!

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps


Top
 Profile  
 
 Post subject: Re: Voltages - too low?
PostPosted: Wed Feb 19, 2020 10:33 pm 
Offline

Joined: Thu Nov 21, 2019 8:14 pm
Posts: 9
Location: Kanata, Ontario
Thank you for your reply.

Yes, I verified that I am using the 120V from the PT (i.e. Black/Red & White/Red). Each 110V is insulated with heat shrink (i.e. Black/White & White/Black).

withOUT tubes, B+1 through B+5: 448, 445, 443, 383, 377

And reducing bias causes the DC voltages all to rise.

- GK


Top
 Profile  
 
 Post subject: Re: Voltages - too low?
PostPosted: Wed Feb 19, 2020 11:50 pm 
Offline
Holy Ghost
Holy Ghost
User avatar

Joined: Sun Mar 13, 2005 4:10 pm
Posts: 7428
Location: Brighton, Canada
would like to know what the AC voltages are, no tubes installed

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps


Top
 Profile  
 
 Post subject: Re: Voltages - too low?
PostPosted: Thu Feb 20, 2020 7:56 am 
Offline

Joined: Thu Nov 21, 2019 8:14 pm
Posts: 9
Location: Kanata, Ontario
with no tubes: 331 & 331 VAC at the diodes (where each Red wire from the PT connects)

My multi-meter only goes to 600 VAC, so I measured each to ground. (Measuring VAC across the two Red leads exceeded the meter ... so I know it was more than 600)


Top
 Profile  
 
 Post subject: Re: Voltages - too low?
PostPosted: Thu Feb 20, 2020 7:12 pm 
Offline
Experienced
Experienced

Joined: Wed Sep 12, 2018 5:17 pm
Posts: 316
Location: Shawnee, OK
Looking at some of the solder joints at the eyelets (especially where there are multiple wires and components connected at an eyelet), it appears some component leads are wrapped around other leads and some eyelets are not completely filled, i.e the power resistors and 47uF capacitors. Also wiring leads (it's okay to leave SOME bare wire exposed) have the insulation very close to the eyelets. Consider reflowing and possibly adding solder to the joints AND having all component and wire leads inserted and soldered into the eyelets. I had problems :bugeye: with my (first) Tweed build due to unfilled eyelets and lugs. Had to remove leads, use the solder sucker, and resolder. One bad connection can lead to lots of problems. Best of luck and hoping you get your voltage issues resolved.

_________________
"The only problem with being retired is you never get a day off"


Top
 Profile  
 
 Post subject: Re: Voltages - too low?
PostPosted: Thu Feb 20, 2020 11:37 pm 
Offline

Joined: Thu Nov 21, 2019 8:14 pm
Posts: 9
Location: Kanata, Ontario
Thank you for your suggestion.

I removed the wires & leads from B+1 through B+5. Used the solder sucker. Then re-installed the wires & leads and re-soldered those 5 eyelets. (photo of the improved results attached).

I also re-flowed the solder in the eyelets with the 6 diodes on the left hand side. And re-soldered the red lead connecting the joined diode pair to the standby switch.

The voltages at B+1 through B+5 remained unchanged.


Attachments:
DSCN1698.JPG
DSCN1698.JPG [ 2.97 MiB | Viewed 902 times ]
Top
 Profile  
 
 Post subject: Re: Voltages - too low?
PostPosted: Fri Feb 21, 2020 9:24 am 
Offline
Friend
Friend

Joined: Fri Aug 16, 2019 4:17 pm
Posts: 38
Location: Detroit, MI, USA
Hi George. I'm far from an expert, but that's never stopped me before. Here's what I can make of the numbers you posted:

Your DC current through R43 looks to be about 16mA with tubes installed ((416V - 408V) / 500R = 16mA), and about 6mA without tubes ((448V - 445V) / 500R = 6mA). For comparison, the callouts on the schematic suggest about 8mA DC with tubes. Your R43 currents seem high.

You also have about (408V - 400V) / 1k = 8mA DC through R44 with tubes, and (445V - 443V) / 1k = 2mA without. The schematic calls for a 7V drop across R44 (i.e., 7mA through R44, with tubes). Without tubes, it looks like the only thing drawing current from B+2, B+3, B+4, B+5 should be R47. This works out to a little over 2mA DC through R43 and R44 without tubes. In other words, your R44 currents look about right.

So your B+2 current is about (16mA - 8mA) = 8mA with tubes, when we'd expect something closer to one or two mA.
And your B+2 current is about (6mA - 2mA) = 4mA without tubes. Without tubes, I don't think anything should be drawing current from B+2.

I'd look super-carefully for anything that might be drawing B+2 current. If you can't find anything, then maybe C32 is leaky? To check that, you could try disconnecting C32, powering up with no tubes, and seeing if your current through R43 drops down to ~2mA. Once that was sorted out, and the no-tubes voltages were looking more sane, I'd install tubes and double-check the bias on V4 and V5.

Disclaimer: this advice is worth what you paid for it. :)


Top
 Profile  
 
 Post subject: Re: Voltages - too low?
PostPosted: Fri Feb 21, 2020 11:12 pm 
Offline
Experienced
Experienced

Joined: Wed Sep 12, 2018 5:17 pm
Posts: 316
Location: Shawnee, OK
George, sorry suggestions didn't help. Keep posting, some one will put you on the right track. And if a solution occurs, please post it so others can learn.

_________________
"The only problem with being retired is you never get a day off"


Top
 Profile  
 
 Post subject: Re: Voltages - too low?
PostPosted: Sat Feb 22, 2020 9:59 pm 
Offline

Joined: Thu Nov 21, 2019 8:14 pm
Posts: 9
Location: Kanata, Ontario
Thank you Hankules for your encouragement.
I am glad that I re-did the B+1 through B+5 eyelets. A couple of them gave me some trouble the first time and they looked a bit dodgy. It went a lot more smoothly when I re-did them.

lighthouse - I followed your suggestion and I disconnected C32 (at the ground side). Without tubes, the B+1 through B+5 voltages were: 454, 453, 451, 391, 385

Comments anyone? Should C32 be replaced?

-GK


Top
 Profile  
 
 Post subject: Re: Voltages - too low?
PostPosted: Sun Feb 23, 2020 2:03 am 
Offline
Experienced
Experienced

Joined: Sat Dec 04, 2010 3:42 pm
Posts: 498
Location: Qualicum Beach, BC
It's been all good advice so far. Glad you redid the B+ connections. It's one less thing to worry about.

If disconnecting C32 causes the no-tubes voltages to rise, then I would suspect that it's a bit leaky and should be replaced. Assuming that there isn't anything on or under the board that's causing a bit of a short.

You could try swapping in one of the other 47uF capacitors at the C32 location and see if that makes any difference. Try C35 and just leave the C35 location empty for now.


Top
 Profile  
 
 Post subject: Re: Voltages - too low?
PostPosted: Sun Feb 23, 2020 11:41 pm 
Offline

Joined: Thu Nov 21, 2019 8:14 pm
Posts: 9
Location: Kanata, Ontario
Ok. I swapped C32 with C35.

with no tubes and C35 disconnected, here are the voltages for B+1 through B+5
452, 450, 448, 388 -

with C35 connected:
455, 453, 451, 391, 385

and with tubes in
422, 414, 407, 281, 273

To me, the differences between adjacent points hasn't changed much since my original posting :-(


Top
 Profile  
 
 Post subject: Re: Voltages - too low?
PostPosted: Mon Feb 24, 2020 2:31 am 
Offline
Experienced
Experienced

Joined: Sat Dec 04, 2010 3:42 pm
Posts: 498
Location: Qualicum Beach, BC
B+1, B+2, and B+3 are at 93% of the expected values with tubes installed. That's pretty good. Tube circuitry isn't precise, especially in guitar amps, and generally anything within 10% of the expected voltage is fine.

B+4 and B+5 are at 84%. A bit low, but it won't keep the preamp and overdrive stage from working. As Stephen said earlier, if it sounds good, it is good.

Your AC voltages are very good. You could check to see that the connections to the diodes are good. Also check that the connections to the Standby switch are OK and the switch itself has good continuity when closed. With the Standby switch closed you should read the same DC voltage at the junction of the cathodes of the two diode strings, at both terminals of the Standby switch, at both terminals of the HT fuse, and at the junction of C31 and R43.


Top
 Profile  
 
 Post subject: Re: Voltages - too low?
PostPosted: Mon Feb 24, 2020 6:15 pm 
Offline
Friend
Friend

Joined: Fri Aug 16, 2019 4:17 pm
Posts: 38
Location: Detroit, MI, USA
Hi George,
Nice work. Here's what I got from your Feb 22 post:
Quote:
I disconnected C32 (at the ground side). Without tubes, the B+1 through B+5 voltages were: 454, 453, 451, 391, 385

This looks perfect to me. (454V - 453V) / 500R = 2mA through R43. That's just what we were hoping for. Looking at these numbers I'd say it's a clear smoking gun that C32 is leaky. I'd replace that cap outright.

I didn't quite understand what you wrote in your next post. You said:
Quote:
Ok. I swapped C32 with C35.

with no tubes and C35 disconnected, here are the voltages for B+1 through B+5

I think this means you disconnected C32, then took the cap that was in the C35 spot and soldered it into the C32 spot, then took some measurements (leaving the C35 spot open). Or did you mean that you left the cap that was originally in the C35 spot disconnected, meaning that you hadn't yet soldered it onto the C32 spot? Sorry for needing the explanation.

Regardless, I'm trying to think of things that might damage C32. Would you be willing to tell us what kind of soldering iron you're using, what temperature it's set at (if it's adjustable), and how long you normally keep it on an eyelet when you're making a solder joint?


Top
 Profile  
 
 Post subject: Re: Voltages - too low?
PostPosted: Mon Feb 24, 2020 8:46 pm 
Offline

Joined: Thu Nov 21, 2019 8:14 pm
Posts: 9
Location: Kanata, Ontario
Thank you, mitch m for your suggestion. Earlier, I verified the diode connections. And I confirmed the voltage from where the diodes join, through the Standby switch, both sides of the fuse and to B+1 (junction of C31 & R43). All voltages along that path agreed.

lighthouse - I appreciate your help.

Regarding my Feb 23 post, I meant to say ...
- I removed C32 & C35.
- soldered the original C35 at the junction of R43 & R44 and the corresponding ground
- soldered the original C32 at the junction of R46 & R47 BUT left the corresponding ground disconnected.
measured: 452, 450, 448, 388 -
- connected the ground for the capacitor
measured: 455, 453, 451, 391, 385
- tubes back in
measured: 422, 414, 407, 281, 273

Is that a better explanation?

I used a Hakko FX888D @700F. I heated the joint just long enough for the solder (which I placed at the circumference of the eyelet 180 degrees from iron) to melt. So about 3-5 seconds for the solder to melt plus a few seconds to fill the eyelet.

I will see if I can get a replacement cap.
- GK


Top
 Profile  
 
 Post subject: Re: Voltages - too low?
PostPosted: Tue Feb 25, 2020 3:31 pm 
Offline
Experienced
Experienced

Joined: Sat Dec 04, 2010 3:42 pm
Posts: 498
Location: Qualicum Beach, BC
That's what I thought you meant in your earlier post. But you didn't see much, if any, improvement with the capacitors swapped or the suspect one disconnected at R46/R47.

It wouldn't hurt to replace the suspect capacitor, but it's unlikely you damaged it.

Check the connections to V1 and V2 and make sure there isn't anything on or under the board, or in the wiring anywhere, that could be causing a short.


Top
 Profile  
 
 Post subject: Re: Voltages - too low?
PostPosted: Sat Feb 29, 2020 9:35 pm 
Offline

Joined: Thu Nov 21, 2019 8:14 pm
Posts: 9
Location: Kanata, Ontario
Well, it helps if I bias the amp while using the Voltage setting on my multimeter. :-)

I probably read and re-read page 90 of the Builders Guide more than a dozen times and still promptly set my meter to measure amperage. :-( Finally, I realized my error.

I found a pair of 6V6s that were a better match and biased them at 22.0 & 21.7 ... measuring mV this time.
Now B+1 through B+5 are: 432, 428, 419, 292, 283

I also re-checked my connections for V1 & V2. No change. And I didn't change the capacitor because ...

I scoured the OSD posts and found 4 other builders where their amps showed the difference between B+3 & B+4 was 120-130 volts (instead of roughly 100 as shown in the Builders Guide). This is the same behaviour as my amp. I guess it is more common than I originally thought.

So ... I decided that today is an auspicious day to put the chassis in its head shell and call it done.

Thanks to all who posted suggestions and encouragement.

- G.

PS
Now I am anxious for warmer weather so that I can build a matching speaker cab.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 21 posts ]  Go to page 1, 2  Next

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 0 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group