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I didn’t like having a post P.I. Master Volume, I thought the distortion sounded harsh compared to the pre P.I. master volume. I decided to put a resonance control in the negative feedback loop. It works okay. I liked the 0.003uF in the P.I. stage, I tried 0.01uF and it was too big. I then...

I don’t think you will find anything. Though it’s not a good sign if the socket is going really dark with heat particularly between pins 2 & 3. If the socket was faulty it would be very dramatic. I would check your 470 ohm screen grid resistors while you are in there. Regards Mark

I would like to have heard an Altec in a Mark 1 amp. Regards Mark

Send an email Alan, I have found that to be effective. As stated by Jay there is a lot of current going through those resistors, but the resistance is very low. Ultimately, I suspect the resistors are there to protect the transformer. A fault which can occur (happened to my Mark 1 amp) is there...

Can you supply a photo? I had a look at a circuit diagram and I couldn’t find where the resistors are. Regards Mark

I don’t have a blown speaker, but this was the first obstacle I could imagine to doing a proper job. Being as curious as I am, I had to ask the question. Regards Mark

I’m contacted Great Plains Audio and they don’t make a 417-8 speaker. Regards Mark

I imagine alignment of the cone is critical, how do you ensure the cone isn’t rubbing? Regards Mark

Thanks for your feedback. I’m wondering if it would be a good fit as an Altec speaker isn’t available anymore. Regards Mark

Thanks for telling me if your experience with these speakers. Regards Mark

I have a Boogie Celestion speaker is my modified SOB, it sounds okay, but it doesn’t sound like the Eminence speaker in my old Mark 1 amp, thus the amp doesn’t sound the same. I don’t know if the JBL speakers were that popular in the Mark 1 amps, but the Altec speakers as far as I know have a...

I asked Mike B about the effects loop he fitted to Mark 1 amps but he referred me to the circuits in the reissue and the Kingsnake. The circuit that he did to amps back in the day is very different to the effects loop that is in the Mark 1 reissue amps. The master volume preceded the effects...

The Mark 1 amps never came with an effects loop. The only Mark 1 I know of with an effects loop is the reissue, and the Kingsnake, as far as I can tell the loop is the same in the reissue and the Kingsnake. I probably would go with something like the Valve Wizard effects loop. Regards Mark

Hi Trenken, thanks for your reply and pictures. One thing I have found with my amp is the ceramic caps sound better than silver mica caps. I have taken silver mica caps out of my amp and reverted to ceramic caps as it diffused the treble somewhat. Regards Mark

Hi David Thanks for your reply. I did contact Mesa Boogie and exchanged emails with Mike Bendinelli on the topic of effects loops and below in italics is the reply. As you can see it’s more or less a description of the Mark 1 reissue effects loop. I’m sure both loops work well, I tend the...

I have the same holes in my SOB awaiting an effects loop. I have a few circuits in mind but I was wondering what Mesa Boogie considered a suitable circuit. August is a long time to wait for a circuit diagram ;) Blue bug has a good circuit in his Mark 1 amp. Valve Wizard loop I have a reverb...

I would like to see pictures of the inside of the chassis. I’m wondering about the effects loop circuit and if the power supply needed another node. The reverb circuit is okay, though I prefer the Fender reverb. It sounded deeper. On my Mark 1 amp, the reverb tank was mounted on the back...

Good luck trying to find those Mallory electrolytic caps. They have been out of production for some time. The 30uF caps look like F&T caps which are fine. I have them in my SOB. Regards Mark

I suspect that it’s a through connection like an Ampeg. One jack is for preamp out which then goes through to power amp in. The reissues didn’t come with graphic EQ. Regards Mark

I thought the Altec speaker was a give away that it’s a 70’s amp. The layout is quite different. The preamp board is different in that there isn’t a dropping resistor and filter cap for a Fetron. The phase inverter has Bassman values in it as opposed to being more Blackface like. I can’t see...