Orange TH30: weird components ?

[maestun]

Hi,
Since there were no schematics available, I've traced most of my Orange TH30 amp (preamp, loop driver, PI, power stage).
For reminder, it's a 2-channel preamp with a quad-EL84 power stage.

I can post my crappy drawings here if anyone's interested, however this amp looks like an EL84-driven Rockerverb 50 MK1 (its schematics can be found online):
- Clean channel: almost identical to RV50
- Dirty Channel: identical to RV50 (except one cathode bias resistor)
- Dirty Shape Control: identical to Dark Terror
- Loop Driver: identical to OR15
- Phase Inverter: identical to OR15

However, I noticed 2 weird things:
- The bass pot (in the Clean Channel tone stack) is a linear 250k pot, whereas it's a logarithmic pot in all the Orange tone stacks I've seen yet
>>> could that be an error made at the plant ? I already noticed that the bass control was not very "responsive"...

- For each EL84 valve, there's a 2k2 input resistor coming from the Phase Inverter into the valve grid (pin 2)... except for one valve, where this input resistor is only 1k !
>>> here, I'm kind of lost, why change this on only one of the 4 valves ? Crappy biasing for bad factory valves ?

Any advice would be very appreciated, thanks

[Chuck H]

The bass pot taper might be an error or a substitution to fill an order. It might also be a spec difference for that particular model to voice it right at moderate control settings. Impossible to know. The single 1k power tube grid stopper is almost certainly an error. Wrong resistor in the tub and it was grabbed without double checking? But also a possible parts substitution to fill an order. There's no voltage division with the grid stoppers so it's not a bias bandaid. I would be surprised if the QC checklist includes individual tube bias test and correction anyway. Try an audio pot for the bass control and leave it in there if you like it better. Definitely correct the odd grid stopper.

[Jazz P Bass]

The Treble control is 250KB.

Check that the two were not inverted.

The older OR amps (quad EL84) used a 1K grid stopper.

Newer ones went to the 2.2K.
There is no reason for having them mismatched.

Note: I have always had help from Orange simply by calling them.
If in doubt, go that route.

[maestun]

Hey guys, here's what I did following your advice:

- Replaced the bass pot from B250K to A250K (treble pot was the right value, ie. B250K). The bass control now works way better, the clean channel had way too much bass response before this fix. Great !

- Replaced the 1K grid stopper with the 2K2, like its sisters, for the sake of symmetry. Doesn't seem to change anything (as expected).

- Also, I replaced R21 from 1K5 to 2K2 (dirty channel's 3rd stage cathode resistor) to exactly match the Rockerverb preamp. The sound seems fuller, chunkier to me - gonna keep it like that !

Last thing I have to mention: the soldering quality on this amp's PCB was terrible. Cold joints, flux residues, a capacitor had its pins way too long... the 4th gain stage plate pin wasn't event fully soldered, the amp was luckily working due to a bad contact. Has to re-solder about 10 points. So I guess a very poor quality control occurred at the factory. Quite shameful for a 900€ amp.

[Chuck H]

[QUOTE=maestun;399920]Hey guys, here's what I did following your advice:

Amps get made every day of the week. That one was clearly done on a Friday

[Jazz P Bass]

Last thing I have to mention: the soldering quality on this amp's PCB was terrible. Cold joints, flux residues, a capacitor had its pins way too long... the 4th gain stage plate pin wasn't event fully soldered, the amp was luckily working due to a bad contact. Has to re-solder about 10 points. So I guess a very poor quality control occurred at the factory. Quite shameful for a 900€ amp.

Orange Amplifiers certainly does not have a lock on crappy soldering.

For a while there I held Peavey at the top of my list of good soldering.
Not so much here of late.

Maybe there is a 'Wave Solder Operator Club'.
They get together & see who can come up with the cleverest way to zip things through the machine.

Preheat Time be damned!

[Enzo]

Or soldered surfaces were not well cleaned before going through the wave machine.

How many times have I had to clean off and resolder the small bridge Marshall uses to run the preamp tube heaters? Solder never took to the bridge legs when it was made.

[Chuck H]

Just ask Stan... Commercial soldering is always better than whatever amount of attention you think it needs And resoldering stuff causes more problems than it fixes. It should never be suggested as a means of repair.