Reconnect the primary leads. Disconnect the two yellow leads ***AND*** the two brown leads. You can leave the two center tap wires connected to chassis. Now connect the power cord straight into the wall. Fuse blow? If so the PT is bad.
UPDATE: Finished my Express build last night > it's working!
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Re: Finished my Express build last night, odd voltage issues (fuses blowing)
https://sluckeyamps.com/index.htm
Re: Finished my Express build last night, odd voltage issues (fuses blowing)
Yep. Disconnected the 6.3v and 300v taps. Same result.martin manning wrote: ↑Sat Dec 03, 2022 6:48 pm The primary DC resistance will be very low, a few ohms. Does the fuse blow with all secondaries disconnected?
Could I have my power switch wired wrong or have the wrong type?
Re: Finished my Express build last night, odd voltage issues (fuses blowing)
The fact that you got voltage readings on the tubes eliminates power switch wiring. Looks like a bad PT.
https://sluckeyamps.com/index.htm
Re: UPDATE: Finished my Express build last night > new PT, no more fuses blowing, odd output
UPDATE:
I ordered and installed a new PT (Heyboer HTS-5199) and everything fires up without issue (both through the limiter and directly into the wall). Though I don't have any guitar sounds coming through my speakers. That's not to say I don't have sound, however. When I turn the presence potentiometer, I get sort of a static sound through the speakers (think what it would sound like if you dragged a microphone across your pant leg), and a hum. So clearly there's output to the speakers (I've opted to wire a jack for each impedance, 4/8+8/16).
I'm using shorting jacks for my speaker jacks and have them grounded to the chassis (metal washers). My common lead (black) from my OT (Heyboer HTS-5200) is going to the ground lug of my 8 ohm speaker jack. I noticed that I'm getting continuity with ground across all jack contacts (I'm assuming that's from the centre tap being connected internally with the 4, 8, and 16 ohm taps and then the CT going to ground). Is that normal?
My center tap (Red) is going to my standby switch, as per the layout I'm using.
Judging that I have signal through my speakers from the presence control, I'm thinking my signal is getting dumped before the OT. Does that sound like what's happening?
I ordered and installed a new PT (Heyboer HTS-5199) and everything fires up without issue (both through the limiter and directly into the wall). Though I don't have any guitar sounds coming through my speakers. That's not to say I don't have sound, however. When I turn the presence potentiometer, I get sort of a static sound through the speakers (think what it would sound like if you dragged a microphone across your pant leg), and a hum. So clearly there's output to the speakers (I've opted to wire a jack for each impedance, 4/8+8/16).
I'm using shorting jacks for my speaker jacks and have them grounded to the chassis (metal washers). My common lead (black) from my OT (Heyboer HTS-5200) is going to the ground lug of my 8 ohm speaker jack. I noticed that I'm getting continuity with ground across all jack contacts (I'm assuming that's from the centre tap being connected internally with the 4, 8, and 16 ohm taps and then the CT going to ground). Is that normal?
My center tap (Red) is going to my standby switch, as per the layout I'm using.
Judging that I have signal through my speakers from the presence control, I'm thinking my signal is getting dumped before the OT. Does that sound like what's happening?
Last edited by prairie on Tue Dec 13, 2022 4:26 pm, edited 1 time in total.
Re: UPDATE: Finished my Express build last night > new PT, no more fuses blowing, odd output
Look at your schematic. If when you say "center tap/common from my OT", those are two different leads. Your OT PRIMARY CENTER TAP should be connected to the power supply filter cap node (80 uF). This will deliver supply voltage to your power tube plates. What voltage do you probe on your EL34 pin 3?
Your OT SECONDARY COMMON should be grounded, fine with the speaker jack ground.
Scratchiness on the Presence control is "normal".
Just plug it in, man.
- martin manning
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Re: UPDATE: Finished my Express build last night > new PT, no more fuses blowing, odd output
good!
A scratchy presence pot is normal for this circuit, but you still have something wrong somewhere.prairie wrote: ↑Tue Dec 13, 2022 3:50 pmThough I don't have any guitar sounds coming through my speakers. That's not to say I don't have sound, however. When I turn the presence potentiometer, I get sort of a static sound through the speakers (think what it would sound like if you dragged a microphone across your pant leg), and a hum. So clearly there's output to the speakers...
Are unused taps still shorting the output to ground when you plug into any one of them? That won't do.
Are you talking about the secondary? There is no center tap. Sounds like you have 4, 8, and 16 ohm taps and a common.prairie wrote: ↑Tue Dec 13, 2022 3:50 pmMy center tap/common from my OT (Heyboer HTS-5200) is going to the ground lug of my 8 ohm speaker jack. I noticed that I'm getting continuity with ground across all jack contacts (I'm assuming that's from the centre tap being connected internally with the 4, 8, and 16 ohm taps and then the CT going to ground). Is that normal?
That could be DC on the presence pot getting to the speaker directly via the feedback loop.
Re: UPDATE: Finished my Express build last night > new PT, no more fuses blowing, odd output
Apologies, my Common from the OT is going to the ground lug of my 8ohm jack. The center tap (red lead) is going to the standby switch.ViperDoc wrote: ↑Tue Dec 13, 2022 4:04 pmLook at your schematic. If when you say "center tap/common from my OT", those are two different leads. Your OT PRIMARY CENTER TAP should be connected to the power supply filter cap node (80 uF). This will deliver supply voltage to your power tube plates. What voltage do you probe on your EL34 pin 3?
Your OT SECONDARY COMMON should be grounded, fine with the speaker jack ground.
Scratchiness on the Presence control is "normal".
Re: UPDATE: Finished my Express build last night > new PT, no more fuses blowing, odd output
Another update!
I disconnected the shorting jacks last night and replaced one with a non-shorting jack (and then wired the 8 ohm tap directly to it, common to the ground lug of the jack). I was able to get guitar signal through the speakers, though it was very quiet (with the volume control nearly maxed, it was at talking level) and pretty muffled. No more hum, though, so I'll call that progress!
I'm going to try and replace all jacks with non-shorting ones, try a new set of power tubes (I'm using a pair of used ones pulled from another amp for testing), and see what difference is realized.
I went through each connection as well to make sure nothing was wired in the wrong spot and that all connections were solid and with good contact. Everything looked good on that front.
I'll report back once I've changed out the power tubes and the speaker jacks.
I disconnected the shorting jacks last night and replaced one with a non-shorting jack (and then wired the 8 ohm tap directly to it, common to the ground lug of the jack). I was able to get guitar signal through the speakers, though it was very quiet (with the volume control nearly maxed, it was at talking level) and pretty muffled. No more hum, though, so I'll call that progress!
I'm going to try and replace all jacks with non-shorting ones, try a new set of power tubes (I'm using a pair of used ones pulled from another amp for testing), and see what difference is realized.
I went through each connection as well to make sure nothing was wired in the wrong spot and that all connections were solid and with good contact. Everything looked good on that front.
I'll report back once I've changed out the power tubes and the speaker jacks.
Re: UPDATE: Finished my Express build last night > new PT, no more fuses blowing, odd output
You don't need to replace the jacks. Just remove the jumper between the sleeve and switch lugs.
https://sluckeyamps.com/index.htm
- martin manning
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Re: UPDATE: Finished my Express build last night > new PT, no more fuses blowing, odd output
Yes. The speaker should be the only load connected to the secondary, and the unused taps should be open (unconnected).
Re: UPDATE: Finished my Express build last night > new PT, no more fuses blowing, odd output
Beautiful. I’ll make the revision and report back!martin manning wrote: ↑Wed Dec 14, 2022 3:08 pm Yes. The speaker should be the only load connected to the secondary, and the unused taps should be open (unconnected).
Re: UPDATE: Finished my Express build last night > new PT, no more fuses blowing, odd output
Corrected the output jacks, put a set of new EL34’s in and biased them, and while I’m getting more signal, it’s still very quiet. Like no louder than moderately loud talking. And it’s pretty muffled too.
Any ideas?
Any ideas?
Re: UPDATE: Finished my Express build last night > new PT, no more fuses blowing, odd output
This is sorta a scientific wild a$$ guess based on it being quite and muffled. Maybe the tone stack is not wired correctly and or has a bad pot or something. Try lifting the tone stack out of the circuit by disconnecting the mid pot from the ground buss. Does that change anything?
Mike
Mike