Tone shift on #124 build after 30-40 mins of playing

[ChrisM]

Hi Bob,

What tubes are you running in V1 and V2? Try some high gain JJ ECC83S. Also, use a balanced in V3 and set the trimmer to a baseline of about 15K between the plates to start tweaking from.

I would put the 100K pot in for the OD drive. Have you compared between it and the unique 250K in 124? I have NEVER preferred 250K in any build, except HRM.

Let us know!

124 uses 250K for level and 100K for drive. That's what I was told?

[BobW]

Stage voltages were confirmed last night using 2 calibrated true RMS meters,
Before the performance, left stage (my side) and right side both measured 117 vac.
During the performance, left side and right measured a low of 106 vac and averaged 108 vac.
After the performance, voltages returned to 117 vac.

Definitely an issue when the average voltage is off by 10%. Also I noticed the lights (big power consumption) would pulse brighter, indicating an unbalanced source.

Chris,
The Presence pot value was a typo, 1.97K not 4.97k.

Dogears,
V1 and V2 are JJs but are not high gain. I have others to try, in V3 as well.
The balance pot is currently a 10K, will tryout a 15K and the 100K in the OD Drive.

thanks for the suggestions

[Structo]

WOW!

That is a huge discrepancy in the voltages.

106 vac and 108 vac, one can only imagine what your secondary voltages were let alone the heater voltage.

If it is a straight 10% less in the secondary that would mean you were only getting about 5.67 v on your heaters.

[Guitarman18]

ChrisM wrote:

124 uses 250K for level and 100K for drive. That's what I was told?

It's a little confusing but the OD controls are:

Either 250K Level and 100K Ratio

or AKA 250K OD Drive and 100K OD Level/Volume

dogears mentioned in his post that the 250K OD drive is one of the unique features of #124 and not to his taste.


Look at ODS-101-NON-HRM in the files section for a more standard value D'clone.
https://tubeamparchive.com/download/file.php?id=1178

Hope this helps,


Paul.

[UltraHookedOnPhonix]

BobW,

If you play out a lot make sure to bring a wall socket tester like the one they have at Mouser (part #: 569-ST102A). A really useful tool all gigging musicians should carry with them in their gig bags. Now you KNOW if the hot, neutral and ground are correctly wired.

Dogears,
Thanks for the Vreg comparisons!

[Structo]

Yep, that little item should be in every gig bag.

[BobW]

Ultra, that is a good tip for anyone, and an item I've had in my briefcase for years. I think the tester I have is just 3 neon bulbs in a similar plug, but does the job. I may start carrying a DMM too.