First post, my “new” 18W

geoff 1965 · Post by **geoff 1965** » Tue 05/21/19 6:24 am

yeah i understand skydog, i've been looking myself and can't work out which circuit the second channel is! it looks to be plexi/TMB but then there's the areas that he's played with the attenuation that are'nt!
if you decide to take it to an amp technician think positively,you've got around $850 in the amp but what you will have is a hand wired point to point combo as good as any marshall 1974X which bye the way are over $3000 to buy!
if you decide to do it yourself then we are here to help and "if in doubt ask" and rather than trying to do the whole amp in one go i've found it helps if you divide the amp into sections like grounding,power section,preamp etc. and focus on one area at a time.
good luck
p.s. just an idea,remember the 1K colber that had failed,do you have any spare el84's to try?

Skydog6653 · Post by **Skydog6653** » Tue 05/21/19 7:01 am

I have the two Mullard/Russia tubes that came with it, before I swapped in the new JJ's.

Skydog6653 · Post by **Skydog6653** » Tue 05/21/19 7:50 am

Before takingit to a tech, I would really like to at the least, replace the components I errantly installed. Of the three larger caps, the one on the left is 50v as was the original. The other two are 500v each. The 0.022 caps were 400v. I didn't use the 100v ones on the invoice, those were ordered by mistake. So, if anyone is willing to help me, which components are in need of swapping out? I'll gladly try and answer any questions on values.

geoff 1965 · Post by **geoff 1965** » Tue 05/21/19 7:55 am

okay so with the new JJ's and 1K's they should be good,you just need to address the resistors & coupling caps,the link for antique electronics supply Josh added has both 1W carbon film resistors and mallory 150's coupling caps rated at 630V.
the power section will need 2 100K and 2 8K2 carbon films and 2 mallory 150's .01uf's "10n" to put right,if you get mallory 10n's for the old polypropylene's you replaced and the preamp .0047uf coupler you will keep the original tone.also swap the 2 100K metal oxides for the preamp plates for 100K 1watt carbon films.

A9A61785-8D7E-4A53-AC83-E8FC9D0EC18A.jpeg

roadshow · Post by **roadshow** » Tue 05/21/19 8:46 am

Skydog6653 wrote: ↑
Mon 05/20/19 10:54 pm
I like to think that I'm not throwing in the towel, rather I'm waving a white flag! I understand your suggestions, but I'm a soon to be 66 year old

I hear ya, surrender for help is good.

I'm pushing 64 with multiple degrees myself and while I like learning have no desire to be tested. Ever. Again.

Skydog6653 · Post by **Skydog6653** » Tue 05/21/19 9:43 am

roadshow wrote: ↑
Tue 05/21/19 8:46 am

Skydog6653 wrote: ↑
Mon 05/20/19 10:54 pm
I like to think that I'm not throwing in the towel, rather I'm waving a white flag! I understand your suggestions, but I'm a soon to be 66 year old
Same here on the testing! I'm learning here. When I started this project, I was tentative about opening up the amp. I've learned to ID the caps, how to drain them and test for the presence of voltage. You wouldn't change a chain saw chain while it was running, right?!

Skydog6653 · Post by **Skydog6653** » Tue 05/21/19 9:46 am

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Here is what I have in the cart. Anything I've missed? (The first two items are 5 pk.)

geoff 1965 · Post by **geoff 1965** » Tue 05/21/19 10:01 am

look's good skydog! i'll be happier seeing those 630V's on the power tubes,400V is'nt enough,your plate voltage on the el84's is 329 when the amp is stable but when you switch on you will have a surge of over 400 volts.
get a sprague atom 25uf/50V electrolytic to try on your channel 1!

Skydog6653 · Post by **Skydog6653** » Tue 05/21/19 11:20 am

All ordered with the addition of the 25uf 50v SA cap. Thanks, Geoff!

geoff 1965 · Post by **geoff 1965** » Tue 05/21/19 12:00 pm

you're welcome,
when you get the parts focus on the power section then have a look at this layout showing the wiring for the channel 1 pots "trem mod" bear in mind the position of the "10n" across the pots not on the turret board.the 25uf on the cathode will give you the full marshall tone and the trem mod is a lot better.

18W_LITE2B_LAYOUT_BrownNote_TRANS_FINAL_v1.1.jpg

note; when tweaking this tonestack the "10n" adjusts bass and has an opposite effect in this position i.e. to add more bass lower the value to 4n7 or to cut bass increase it to 22n.you should be good with the 10n and 10n into the phase inverter.
if you're unsure with anything just ask,
good luck

Skydog6653 · Post by **Skydog6653** » Tue 05/21/19 2:03 pm

I'm a bit confused; isn't 10n and .01uf the same value?

geoff 1965 · Post by **geoff 1965** » Tue 05/21/19 2:07 pm

yeah it's the same value

Skydog6653 · Post by **Skydog6653** » Tue 05/21/19 2:35 pm

I need to print me off a conversion table.
ps, I found this for anyone as green as me! https://www.digikey.com/en/resources/co ... apacitance

For resistors; http://hfradio.org/resistor/

Skydog6653 · Post by **Skydog6653** » Tue 05/21/19 5:54 pm

I had found this layout and used it to buy parts before, hence the 0.022uf caps https://valvestorm.com/sites/default/fi ... Layout.pdf

geoff 1965 · Post by **geoff 1965** » Tue 05/21/19 6:39 pm

yeah i have .022's in my power section,it was the voltage rating that was "borderline" if you have 400 volts hitting them every time you switch the amp on it's better to have a safety margin like the 500V & 630V's give you.if they fail and leak DC onto your el84 grids you'll have a serious problem!
here's something else to help you in understanding circuits etc. if you click on "forums" then "18watt technical discussion" you'll see a box at the top saying "search this forum" and just type in a subject.there's a ton of information in there which i don't think most people are aware of! you just have to take the time to read through the posts and take note of the useful info,i've spent hours & hours in there!

Post by **JMPGuitars** » Tue 05/21/19 6:59 pm

I like capacitance charts like this: http://www.electronicsteacher.com/capacitor-chart.php

The code guide shows the relevant codes, so you can figure out the logic behind the numbers, and then you don't need to check the chart as often.

Skydog6653 · Post by **Skydog6653** » Wed 05/29/19 6:09 pm

I installed the new components yesterday. What are the style/type of resistors on the jacks, tubes, & pots? V1 has 4/33.8K R's, V2 has 1/470KR. Each High input jack has a 1M R. The V&T pots on the Marshall channel share a 100 K R. The V pot on the TMB channel has a 83 K R. Should I retain this setup as is? @Geoff 1965 which cap does the 25uf 50V take the place of? The amp still has a noticeable hum to it that goes up with the V knob. It did not squeal but when I put it on standby there was a “microphonic” pop. Sorry, I don't know how else to describe it. I feel like I'm getting there!

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Post by **JMPGuitars** » Wed 05/29/19 7:01 pm

Your ground scheme is still a little off. The pots and preamp section should be grounded near the input jack. It should not be grounded near the power amp section or transformers. Non-insulated wire should only be used on the buses. It should not be used free floating from the pots to the ground as it is currently. Make sure your pots and inputs are only grounded once, and all together via/near the input jack.

See my post for more info, and associated layout here: viewtopic.php?f=4&t=25372

Thanks,
Josh

geoff 1965 · Post by **geoff 1965** » Wed 05/29/19 7:44 pm

hello skydog,
the resistors on the jacks and tube sockets are carbon film and should be okay,i've circled in "white" where the capacitor 25uf/1K5 resistor go,check the wire goes to pin3 of V1 and remember the positive side of the capacitor goes to the tube socket.
there is a couple of area's you need to address, if you replace the large corbon comp resistor with a new carbon film 8K2 like you've done on the other side "circled" that will make the power section good.
also the green 8K2 next to the 1K's was a wirewound B+ dropper and it looks like you've replaced it with a 1W carbon film,you need to put the wirewound back in there or use a new 2 or 3 watt metal film.just check the turrets i've circled in "red" are not joined together,it's hard too see on the pic.
also check the sozo cap has a good connection to both turrets,what wattage is your soldering iron?

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Skydog6653 · Post by **Skydog6653** » Wed 05/29/19 8:37 pm

I am waiting on a replacement iron for my Hakko 936. I was trying to get by with a 30W China special. I know some of the joints look bad. I'm going to remelt them with the new iron.

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