trouble with used 1987x (1992 -> no FX Loop)

philip · Post by **philip** » Thu Aug 09, 2007 6:13 pm

I just got me a used 1987x and am a little confused right now. I tested a new one and that blew me away, but this used one just isn't sounding right.
It doesn't have the "on demand" feedback that I loved on the new one, and, what's even more disturbing; it's got some strange things going on when playing distorted: there's this nasty, fuzz-like saw thing going on,
it seems to hover above the note, changing slowly, almost
phaser-like. Also the bass notes get farty, buzzy and boomy...
Though that last bit has improved with different power tubes and a biasing.

When it's clean (volumes under 2), it sounds real good, both with a Strat or a Les Paul (with the Strat it's closer to SRV than I ever got before), but turn up the volumes and damn, that's not the full singing tone I heard from the new 1987.

I had it open today and apparently someone removed the 500pF cap parallel to one of the resistors that join the channels.
Also the resistors between the power tubes and ground are 10k, not 1 Ohm. Everything else seems to be stock.

Any ideas what I might be experiencing here? What could it be?

I am now waiting for some NOS Brimar ECC83, a metro PTP board that I ordered and some new filter caps... (somehow I don't trust 15 year-old filter caps)

sometimes I think I should probably just try to sell it again and get a new one, but on the other hand it should be possible to get some sweet tone out of that thing. No?

Thanks in advance to everyone who is willing to shed some light on this mystery.

cheers,

philip

jbzoso2002 · Post by **jbzoso2002** » Thu Aug 09, 2007 8:24 pm

sound like filter caps are bad. so if you do what your saying
it should fix the prob. also look into a choke and an output
transformer.

jimmy

toner · Post by **toner** » Fri Aug 10, 2007 1:28 am

Your descriptions do sound like the filter caps are going bad, especially about the bass response. That will probably fix it.

You'll have a killer amp once the PTP board is installed. A better OT would help but a lot of people think the stock 50w OT's are pretty good compared to a stock 100w. I replaced my 100w reissue OT and it sounded much better (overall tone, note clarity, etc.).

philip · Post by **philip** » Fri Aug 10, 2007 7:22 am

Oh thanks! That sounds encouraging.
I'll try to hurry up my filter caps order and see if I can probably pick them up tomorrow.

I'll keep you updated.

cheers,

philip

philip · Post by **philip** » Sat Aug 11, 2007 4:22 pm

here's a little update; still waiting for my NOS Brimar tubes, the PTP board, new filter caps... But I had another look into this amp and noticed some weirdness wih the presence pot: the cap was from the left lug to ground, the middle and left lugs were bridged and there was a resistor from the right lug to ground... no idea what that was supposed to do.
I put the cap between the left and the middle lug, grounded the left lug and lost the resistor. While the presence control still doesn't seem to do anything (prolly the pot is over the hill), I feel the sound opened up a bit.

But still I get evil fizzle once the amp distorts. I even found a thread on this forum with a soundclip that comes real close to what I'm experiencing:

Thread: http://forum.metroamp.com/viewtopic.php?t=11377

Soundclip: http://www.frequencybox.com/36-03.mp3

I know I'll rebuild it to PTP with all new components anyway, but I can't let it rest; patience and me, we're just not getting along : P plus I really wan't to find out what's happening here.

philip · Post by **philip** » Mon Aug 13, 2007 4:06 am

BTW, is there a way to test the OT? With a simple multimeter?

philip · Post by **philip** » Mon Aug 13, 2007 2:41 pm

update: the preamp tubes are here. NOS Brimar, they sound a whole lot smoother and "velvety" than the Ruby tubes that were in there, but the scratchy/fizzy distortion problem persists...

Filter caps are next, should be here by wednesday...

...is it even possible that a defect OT shows such symptoms?

philip · Post by **philip** » Tue Aug 14, 2007 6:59 pm

ok, put new filter caps in tonight. Unfortunately that wasn't it...
Tone has improved, got clearer, but the bad broken amp sound is still there when distorted...

I guess tomorrow my PTP board will be here, I'll see if I can drop it in tomorrow night.

philip · Post by **philip** » Wed Aug 15, 2007 4:36 am

just had a thought; with the presence control not working, is it possible *that* is causing this scratchy stuff? Oscillations maybe?

To try this out without a new pot, what would I do? Just remove the cap temporarily?

philip · Post by **philip** » Thu Aug 16, 2007 6:34 am

received my PTP board yesterday and started putting the components on it. Hopefully I'll have time to swap the boards tonight.

philip · Post by **philip** » Wed Aug 22, 2007 7:10 am

ok, I put the PTP board in last thursday night. It went almost smooth, only I experienced a very low output due to the mix-up of a 470 Ohm resistor for a 470 kOhm... while trying to find out what was wrong, I got zapped at 4:30 am ... coffee does a much better job to wake you up LOL no harm done though

now this monday I finally played it in rehearsal.
I love it now!! For my taste it could give feedback earlier, but the tone is neat.
I kept the bright cap; after experimenting without one and swapping it for a 500p, I liked the 100p best (a silver mica though, gotta try a ceramic too).
But I changed the "fizzy" cap to 100p.

The normal channel isn't working yet, need to find out why that is (probably a wiring f'up on the input jacks...)

While doing all my soldering I noticed that it had some mods before, for example the inputs were wired differently; two shielded cables directly to V1... what was that supposed to do?

Anyway it sounds sweet now, with the Volume on 7-8 I have great control with the guitar's vol pot, and it almost nails Allman Brothers, AC/DC, Clapton /w Cream... plug in a Strat and you have instant Jimi or SRV. Unbelievably versatile amp.
And it goes very well with my limited JH Stack Cab

...now I wonder what an OT upgrade would do tone-wise...

neikeel · Post by **neikeel** » Wed Aug 22, 2007 7:18 am

philip wrote:
...now I wonder what an OT upgrade would do tone-wise...

On this amp relatively little bang for your buck! Iwould get it FULLY sorted before doing this

.

But if you want to add a cherry to the top of your cake I recommend the Marstran followed by George's Heyboer. Still undecided by my MM

.

philip · Post by **philip** » Mon Aug 27, 2007 4:57 am

the normal channel is working again. It wasn't the inputs but a broken .0022

neikeel · Post by **neikeel** » Wed Aug 29, 2007 10:31 am

Quite a few people use a 0.022uF there to stop that channel being too thin. The combination of big mixer bypass cap (470-560) 0.0022uF coupler and 5,000pF bright cap can make things a bit shrill.

Using a 0.022uF coupler and 500-1000pF bright cap suits me better.

Also depends on your speakers tho'. The lead combo above and 70s black backs can be quite harsh. Run the same set up into some golds or blues and the difference is startling - much smoother.

philip · Post by **philip** » Sun Sep 23, 2007 11:19 am

I think I got it!

After adding grid stoppers, a 100k NFB resistor, reverting the grid ressitors to 1k (was 2k2) and adding a 220k resistor to pin 2 of V3 I now redid the PT lead dress and went back to the .0022