Mesa DC30 and heyboer trans.

[Teleman55]

I am considering trying a Heyboer AC30 output transformer in my DC30.I see listings for Original AC30 and Reissue AC30 transformers,but haven't found any specs.Can anyone tell me the difference between them?

[Chuck H]

Excluding actual differences between the original transformers and the new transformers, and so assuming we're talking about newly made transformers for an actual AC30 vs. a reissue AC30, I would think the difference would be mainly in the mounting spacing and primary input voltage taps. I'd bet my a$$ there is no difference in the primary impedance, stack size, inductance, etc. between modern units by the same MFG. So just pick the one that best suits your needs for the amp you plan to install it in.

Chuck

[Teleman55]

Thanks Chuck,By the way I meant to say Mesa DC3.All in all a very cool amp,after a few minor upgrades and mods that have made this a great club amp I figured why not try an OT upgrade and Heyboers get great reviews.

[Teleman55]

While waiting for the tranny to arrive I have a question-I read somewhere that the DC3 Lead channel has a fake tone stack.Could somebody please explain?

[Pedro Vecino]

Yes. In the middle of the four steps it takes a filter like the one that composes a traditional tone stack (bass/middle/treble) with fixed values (resistors as potentiometers).
I dŽont know if the schematic is in the net, but itŽs similar in his structure to that of the Maverick.
Regards

[Teleman55]

Thanks Pedro-If the tone stack is a set of fixed value components what the hell do the tone controls do?

[Pedro Vecino]

Hello. The fixed tone stack is used as a filter in the preamp. Instead of being done with a resistor and capacitor paralleled for example, it uses a more complex system to obtain a particular signal shaping but in essence itŽs the same thing. Other one (the one that you handle) is the real tone stack.


Regards

[Teleman55]

Now that I have the new OT I need help with the speaker connections.The DC3 has 3 speaker jacks-8 ohm,4 ohm,4 ohm.The new tranny has 4,8,and 16 ohm outs.Does anyone have a wiring scheme or diagram? I would like to have an 8 ohm jack,ext.speaker 4 ohm min. and the third jack 16 ohm.All my OT swaps have been direct replacements so I this is new to me.The transformer is from GDS amps.

[Pedro Vecino]

Hello. I dŽont have the schematic but Dc series amps that I know only have two OT taps: one of 4 ohms (connected to both outputs of 4 Ohms) and one of 8, connected to the output of 8.
You can form again the outputs to have three impedances of his OT.
The point of connection for the feedback and the slave out (verify it) is the 8 Ohms tap.
Regards

[Teleman55]

I went with the original speaker jack scheme,and fired the amp up this afternoon.Something sounded wrong and I realised the reverb connections were reversed,a quick swap and all is well.The main difference is the bottom end,tighter and more full,I really have to reset the tone controls.I didn't have a lot of time with it yet and time will tell if I need to tweak any components.I did notice that the power tranny gets hot to the touch,I left it on for a couple of hrs.and with an IR thermometer measured 140 degrees.I had never checked it before so I have no idea if this is a problem.The new OT is at least 30% larger (Heyboer 36wt from GDS) could it be drawing more current? Should I be concerned?

[Chuck H]

The new OT is at least 30% larger (Heyboer 36wt from GDS) could it be drawing more current? Should I be concerned?

The OT doesn't draw current, the tubes do. If you replaced the tubes and didn't adjust the bias then the tubes may be drawing more current than the old ones. Likewise, if you kept the old tubes and did change the bias. If the tubes aren't glowing on the plates (check in a dim light setting) your probably OK. As far as heat, can you hold your bare finger on the PT when it's at it's hottest? If so it's probably OK. One sure sign your PT is too hot would be if you can smell it or potting material is dripping out of it. They also physically hum sometimes when stressed.

Chuck

[Teleman55]

Thanks Chuck,I did change the tubes a while back and did not check the bias.I need to find some info on converting to adjustable bias and what would be a good bias range.Could a transformer change affect bias?