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Re: NOS-style JTM 45/100 on Metro chassis
Posted: Sun Jun 29, 2014 11:01 pm
by Strat78
emmjaydubya wrote:Well I finished the pre board, everything wired in. Soldered a 100k forming resistor across the standby switch as instructed for the 45/100. Brought the voltage up slowly with the variac and monitored individual caps so as not to go beyond rated voltage, got it up to a comfortable 115v wall voltage. Measured across the 100k, NOTHING. Couldn't get a reading at all across the resistor, tried everything. Now I'm confused. I left it forming for about 45 minutes and I noticed a slight smell from the 15uf 450v Erie pre cap and could smell some heat coming off of it as well, which I figured was bad. I decided to shut it down and disconnect the pre cap to see if it was the culprit. Switched power back on with positive leg of the pre disconnected but still couldn't get a reading across the 100k for the PI, screens and mains. What do you guys think? I don't have a clue what to think right now...
I'm kicking myself for not taking better notes during this process, I think I had similar problems as well and it turned out to be something pretty simple. I'm wracking my brain trying to recall.
Re: NOS-style JTM 45/100 on Metro chassis
Posted: Mon Jun 30, 2014 12:03 am
by maxwedge572
Well I don't know about the actual problem is but you won't get jack across the 100k when the switch is thrown on (closed). Why would voltage go through the 100k when it gets a free ride through the switch?
Edit: Never mind me because I think you mean in standby mode and you should see something across the resistor, because the amp is the rest of the load, plus the resistor. If the resistor was the only load then you would see 0v but it's not so you should see a voltage.
Re: NOS-style JTM 45/100 on Metro chassis
Posted: Mon Jun 30, 2014 1:46 am
by neikeel
Strat78 wrote:
I'm kicking myself for not taking better notes during this process, I think I had similar problems as well and it turned out to be something pretty simple. I'm wracking my brain trying to recall.
Nearly always is. Only you can track it down at this stage
Re: NOS-style JTM 45/100 on Metro chassis
Posted: Mon Jun 30, 2014 2:10 am
by emmjaydubya
maxwedge572 wrote:Well I don't know about the actual problem is but you won't get jack across the 100k when the switch is thrown on (closed). Why would voltage go through the 100k when it gets a free ride through the switch?
Edit: Never mind me because I think you mean in standby mode and you should see something across the resistor, because the amp is the rest of the load, plus the resistor. If the resistor was the only load then you would see 0v but it's not so you should see a voltage.
Turns out it's simple all right. I'm a dumb-dumb.
http://forum.metroamp.com/viewtopic.php?f=32&t=31179
Read this thread many times, I looked at Shakti's intructions (3rd post down) and also read Roe's response (6th post down). I soldered the 100k ACROSS the switch (Roe) but also flipped the standby OFF (Shakti). This is where I screwed up. Should have just turned on the power and left it in standby mode. Thanks for making me see my mistake!
SO, did I screw these caps up from being properly formed now since there was no 100k between rectifier and filter and they got full voltage? Seems like I did.
Re: NOS-style JTM 45/100 on Metro chassis
Posted: Mon Jun 30, 2014 6:18 am
by neikeel
The RIFAs will be absoutely fine without forming in the amp. The Erie will be another matter. Try the amp out and not just quick off/on give it a few hours.
Re: NOS-style JTM 45/100 on Metro chassis
Posted: Mon Jun 30, 2014 6:27 pm
by emmjaydubya
Thanks Neil, I have several of the 15uf Eries so I just changed out the pre and began reforming again today, WITH THE STANDBY ON this time.
All of the caps are already below 5v, I'll wait it out till they hit 2v, hopefully this time tomorrow I will be rattling glass! Things are looking good!
Re: NOS-style JTM 45/100 on Metro chassis
Posted: Sun Jul 06, 2014 12:35 am
by emmjaydubya
Re: NOS-style JTM 45/100 on Metro chassis
Posted: Sun Jul 06, 2014 12:51 am
by emmjaydubya
Re: NOS-style JTM 45/100 on Metro chassis
Posted: Sun Jul 06, 2014 12:57 am
by axeman
Wow, sexy. Is the diode by the bias circuit correct?
Re: NOS-style JTM 45/100 on Metro chassis
Posted: Sun Jul 06, 2014 1:09 am
by emmjaydubya
The bias diode goes opposite of the rectifier diodes.
http://plexireplicas.com/metropoulos-am ... block-end/
Re: NOS-style JTM 45/100 on Metro chassis
Posted: Sun Jul 06, 2014 9:23 pm
by maxwedge572
Really nice work!
Re: NOS-style JTM 45/100 on Metro chassis
Posted: Mon Jul 07, 2014 7:34 am
by neikeel
Hard to see how anyone can make a better Marshall clone than that!
Re: NOS-style JTM 45/100 on Metro chassis
Posted: Mon Jul 07, 2014 9:18 am
by bill bokey
Re: NOS-style JTM 45/100 on Metro chassis
Posted: Mon Jul 07, 2014 3:48 pm
by axeman
5,000.00 Amp Whats the part number on those Diodes
Re: NOS-style JTM 45/100 on Metro chassis
Posted: Mon Jul 07, 2014 6:36 pm
by emmjaydubya
Thanks so much guys! I just bought a bias probe from Eurotubes to make biasing a breeze. My 4x12 cabs are at my rehearsal space so I haven't had a load to bias with!
Tonight's the night though, gonna play it with the band for the first time.
neikeel wrote:Hard to see how anyone can make a better Marshall clone than that!
Thank you Neil, I used pics of your amps along with Phil's clone, worked to a high standard indeed!
axeman wrote:5,000.00 Amp Whats the part number on those Diodes
Not sure what the part # is but Valvestorm sells them. Halfway down the 45/100 build checklist page...
http://valvestorm.com/JTM%2045/100%20Kit
