trinityamps.com

A week after the course, I wanted to post my results, but before doing so I wanted to thank
Stephen and Chris again for all their efforts. I can’t say how impressed I am with the
follow-up support, both via email and through this forum.

I should also add that I have an unfair troubleshooting advantage; I have a Tramp combo which Stephen built for me last fall.

When I left last Sunday night, the head was completely wired but I was getting no sound through the
speaker. Both Stephen and Chris looked at it and nothing was obvious.

Since then, I used the chopstick method and found one connection which was bad (from the
volume to the impedance switch). I corrected that and also cleaned up some
of my work. I also spent a few hours double checking everything and cross
referencing to the tramp combo.

I am now getting sound through the speaker but the power level is acting
like a volume pot (at the 6 position there is virtually no sound, at max
position the sound level is virtually the same as the tramp combo but
perhaps a bit thinner). On the Tramp combo, the difference between the 6 setting and max
on the power level to me is more like an audio presence control but the volume level is almost the same.

This testing was done using the same speaker and all controls at the same setting (6 on the dial).
I also swapped tubes back and forth between the head and the combo to ensure it wasn't a tube problem.

I have checked the 2 100K resistors around the Power Level pot and found they were both accurate (I removed the one
attached to the 50uF cap to measure it).

The voltage readings for the two amps are as follows (I used the voltage points from the layout provided).


The last thing I checked was the power level pots. The combo is a split shaft marked B1M. The head has an Alpha marked A1M (does the A mean Audio Taper and if so, would this be a factor?).

Any ideas on the cause of this problem would be appreciated.

Thanks, Scott

Where is the black plate wire (wire from 220K to pin 1) going?

Is the shielded wire from the MV control going to pin 6?


Chris...

_________________
http://pdfelectronics.com

Does your impedence switch have two center lugs like mine does? I instinctively used the "A" terminal. I had the same problem as you, no sound. I bent the other center terminal to touch the "A" terminal. Voila! SOUND!!!

I just used a jumper to connect the two center terminals and it's been working great.

You too have learned something. The difference between audio and linear and how to tell them apart by sound!!

You have a linear pot in there, not an audio taper & not your fault. All it means is a different 'swing' to the voltage as you have already measured. If you want the same swing, I can get you an audio taper (as most are changed to that now).

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

Chris,

I double checked both connections you mentioned;

1) The Black wire from the 220k resistor is going to pin 1 on the preamp tube.
2) The shielded wire from the master volume is going to pin 6 on the power tube.

Stephen,

I thought the power level pot was possibly the problem but your response has confused me. I've understood
audio versus linear pots in the context of a guitar volume control (log taper matching our hearing/perception of loudness), but was unsure of it in a power level control.

The combo you built for me last fall has a power level pot marked B1M which as I understand it is a linear taper.

The kit I received for the course (the DIY head) has a power level pot marked A1M which as I understand it is an audio taper.

Double checking the layout provided, this pot is marked as "POWER LEVEL 1M-L" which could mean linear or log.

Are you saying an audio taper pot is what is now used on the Power level control
"I can get you an audio taper (as most are changed to that now)"
and that I should change the Linear pot in the combo you built for me to an audio taper?

Thanks,

Scott

Hey Scott,
Same idea here as in a guitar pot:
The difference between the Audio/Linear POT is simply the rate they change from Minimum to Maximum value. That said, this is not really causing any real "issues" per say, but you will get different readings at different places in the rotation when comparing the two. The Maximum and Minimum values will still be the same but how they travel between the two will be noticeably different. Hope this helps.
-Dana

Hi Dana,

Thanks for your input, I really appreciate it. It’s interesting comparing the two types of pots and how they work in conjunction with the other controls, most notably the volume/master volume, in terms of the output. I’ve had the combo for a lot longer and am used to the way it works, so when I was testing the amp camp head A/B with the combo, I simply thought there was a problem with the head. Maybe having the combo wasn’t such a trouble shooting advantage after all, although I really learned a lot double checking everything (which was the whole point of the exercise anyway). Now all I have to do is decide which type of control I prefer (and of course build a cabinet). Everything else seems to be working correctly.

Good luck with the mods on your amp. I’ll be interested to hear how you make out with them.

Scott

And if you want the audio control, I'll provide it. Just let me know.

For anyone else too, if you have the 'splined shaft' power control version.

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

The logarithmic or audio pots vary the resistance according to the way the ar hears volume level changes, which is logarithmic and not linear. So you would normally use log/audio pots for any kind of volume or gain control, so the way the volume increases seems proportional and natural to the human ear. Tone controls can be either linear or log/audio.

HTH

_________________
Great tones come in small glass jars!