There is something growing in my basement

[blackba]

mmmm purple!!!

 

[SpiderWars]

I have a few different new production options on hand but since the pF-value caps at Treble/Bright/Bright mixer are so much the voice of the amp I decided to try NOS Lemco dogbones if possible. Hard to find typ Marshall values at reasonable cost tho (any tips/leads appreciated!)

These are bigger than I exected but they are 6kv. I was going to use one for the treble cap and use a 47k slope. They are all 300pF.

But I might use another for the bright channel treble peak and use a 390k resistor instead of 470k...leave the bass channel mixer at 470k. Should have the same knee for the bright channel. I...think.

 

[SpiderWars]

Meh, they fit fine. Those huge silver micas were bigger.

Lots of creative license here.

 

[harddriver]

Before you solder those in there, I built a 69SL with all NOS iskra's, I used a 560pf Modern Ceramic on the 470K bypass cap and an NOS RS Mica 560pf cap in the tonestack and a 47pf lemco dogbone in the PI. The amp was alright but it was more brash and harsh and strident in the highs than I wanted. I still had an NOS RS mica 560pf cap laying around, so I took out the Modern ceramic and installed the NOS RS and bammo!!!! The amp really smoothed out nicely and had a way better tone, I was pretty shocked. I think there was a reason alot of those early 70's metal panels tended to be harsher and more strident in the highs, because of them transitioning to ceramic caps in the bypass and tonestack, whether tan or the Lemco dogbones. My 72 SL was aggressvie and harsh as well, and guess what, it had the 500pf tan ceramic disc cap(it was original to the amp) on the 470K bypass but the amp has a Lemco Mica 560pf cap on the tonestack. I swapped out the ceramic for an NOS Cornell Dublier silver mica 560pf and the amp smoothed out and sounds more like my 68 Metro plexi that has all NOS Lemco micas. The dogbones might sound alright I have not used the 500pf ones, but the tan disc caps I think are the culprits. I also bought two of the brand new SOZO 500pf mica caps that a pretty big but they are claimed to sound like old LEMCO mica's, I have not used them yet so I can't say one way or the other, but it might be an alternative to NOS for you, I also think the dark brown NOS Cornell Dublier's from the 80-90's sound really good.

Here's the amp with all RS micas, I don't have any clips with the ceramic cap in there but it did not sound as good as the mica in the 470K bypass. Amp also has a Lar/Mar with a PEC dual 250K.

 

[SpiderWars]

That sounds really good! Thanks for the tip. I know what you mean about different cap types sounding different. Even different ceramic discs sound different and I agree that the tan disc caps tend to be very aggressive. I don't have much experience with the dogbones but psychdave said one of his favorite 'stock' Marshalls was full of them so I ran with it. I think I can swap them easily the way I have them in there.

I didn't mention it but that big beautiful clean tone is very important too.

 

[harddriver]

That sounds really good! Thanks for the tip. I know what you mean about different cap types sounding different. Even different ceramic discs sound different and I agree that the tan disc caps tend to be very aggressive. I don't have much experience with the dogbones but psychdave said one of his favorite 'stock' Marshalls was full of them so I ran with it. I think I can swap them easily the way I have them in there.

I didn't mention it but that big beautiful clean tone is very important too.

You can try the dogbones, but if you don't like them, I would say the NOS CD or the Sozo's if you can't find any NOS mica caps. I really didn't think one cap on the mixer 470K would kill the tone but it did. Dave Friedman say there are some new Vshay ceramic caps that he likes, I bought some, haven't tried them yet, I can vouch for the NOS CD mica's though.

 

[SpiderWars]

Only laziness and iron can stop me now.

 

[Dr. Tweedbucket]

I can exterminate that right away. Just give me a time and your address. There will be a $500 hazardous waste disposal fee and you have to pay in advance.

 

[SpiderWars]

Jacks set up.

Also did all the underboard wires, power board and Presence. I'm using the 25k Presence plus 4k7 resistor.

 

[harddriver]

It looks like you have some 70's vintage Marshall pots in there, are they old NOS or new?

 

[SpiderWars]

It looks like you have some 70's vintage Marshall pots in there, are they old NOS or new?

The Normal channel volume is a .825M pot from a '76 50W. The bass pot is also from the same amp and is .666M...no way I wasn't using that! I almost always use the lower range of the bass pot in these type amps so that pot seemed perfect. Everything else is new CTS.

I decided to try the old stock Normal volume just because I like the taper and I don't need full-on gain in that channel. I have a pull-pot for bright on the Bright channel volume and I have a feeling I'm going to hate the taper on it.

 

[SpiderWars]

I was looking at grounding schemes and wanted to go with Larry's but I have a dual filter cap for V1/V2 which shares that ground. And I'd really like to ground the screens along with the main caps and rectifier since they share the same board.

So I think I'm going to try:
Power tubes grounded thru 1R resistors at each socket bolt
Power cord Earth at edge cap can bolt
Power board (bridge/main caps/screen caps) ground at other cap can bolt
All grounds for V1/V2/Input jacks/33x2 dual filter/Volumes at bolt near input jacks (see pic above)
Everything else grounded at bolt near choke, under Mid pot (this includes Mid pot/Presence grounds)

Also, there will be a voltage divider on the two PI cap can sections to lift the heaters. So the heater center tap will go there.

Seems weird to have those two ground lugs straddling the PI filter and then run the ground for that filter all the way over to the choke area. Anyway, I think this covers most of Larry's rules for grounding. I originally had another ground point for the bias supply/screens/heater CT but the heater CT 'lift' filter shares the PI filter ground and as mentioned the screen filters share the power board with the main caps/rectifier. So I just shit-canned that whole ground.

 

[panhead]

Id like to know how you got Chris Merren to answer the phone or email. lol

 

[technomancer]

Id like to know how you got Chris Merren to answer the phone or email. lol

Merren answered my email to buy something listed on his website no problem... of course that was five weeks ago and I don't have my iron yet so...

 

[Rick Lee]

Chris was very responsive to me once and I bought a set of iron from him. I gave up trying to buy from him for my next several builds. Just could not get him to respond to my request to spend money with him.

 

[glpg80]

If you share a ground with the cap on mains that’s fine, but know technically it’s supposed to be on it’s own ground. Regardless of where you tie it to chassis ground, be sure a lock washer exists on that nut and screw.

 

[JimAnsell]

was hoping thread would be about mushrooms.

nah, thats my basement

 

[SpiderWars]

If you share a ground with the cap on mains that’s fine, but know technically it’s supposed to be on it’s own ground. Regardless of where you tie it to chassis ground, be sure a lock washer exists on that nut and screw.

Thanks!

I emailed Chris and he emailed back, I paid. I've bought from him before. You never know if your email was the first he read that day or the 200th. So I just try to keep it very concise and then leave him be.

 

[glpg80]

Hell I feel bad. I chatted up Chris about his engineering background for a few hours as he and I have a similar career path and interests. We were talking for ages and no I didn’t order anything lol

 

[SpiderWars]

Hell I feel bad. I chatted up Chris about his engineering background for a few hours as he and I have a similar career path and interests. We were talking for ages and no I didn’t order anything lol

He was very helpful with a previous build using custom OT but this time it was his stock models. I just got a USPS Ship notification from Merren Audio but looks like I won't get it until Monday since Friday is a holiday. I have a lot to do before I really need them.