Metropoulos Forum

OK, my first dumb question on my new 50 watt kit build. Being a novice at amp building (this is my 4th), I am easily confused. So I got to the part in the 50 watt instructions about wiring up the PT (step 6, page 10) to the heaters, and of course the wiring for the Heyboer vs the Mercury is different. The big problem is that the Mercury has about twice as many wires, some that are duplicated.

I'll attach a pic of the two schematics. If one of the more experienced here can decipher it and say "These are the ones to use, Jim!" I'd be grateful. Thanks in advance for any help that can be provided.

Hi Jim

The greens will work for the heaters.

See 6string's build: http://forum.metroamp.com/viewtopic.php?p=124724

It looked to me like either the Gray or Green sets would be fine. But as 'SDM' Steve mentioned, it's possible that both 6.3v windings might find a use. I'd call MM regardless of what worked for who, and be sure to understand the intended purpose.

Will

thousandshirts wrote:Hi Jim

The greens will work for the heaters.

See 6string's build: http://forum.metroamp.com/viewtopic.php?p=124724

It looked to me like either the Gray or Green sets would be fine. But as 'SDM' Steve mentioned, it's possible that both 6.3v windings might find a use. I'd call MM regardless of what worked for who, and be sure to understand the intended purpose.

Will

Yeah, I hear you. I sent the two PT's schematics to both George and Paul at MM to decipher, cuz I figured the same as you, that both could probably be used (separately). Oh well...I guess I'll have to wait for an answer to get going again. I have a big order of speakers coming in late tomorrow afternoon, so I won't be able to work on the amp again after it shows up, and I head out for a week to Austin on Saturday so it would have been nice to wire up the tube sockets and the board before I left.

Oh well... anticipation...LOL

Hey Jim you sure MM gave you the correct PT? Their labeling leaves something to be desired. From that label I would think that is a 45 watt Radio Spares clone not a Drake 118 clone that belongs in a 50 watt with a SS rectifier.

908ssp wrote:Hey Jim you sure MM gave you the correct PT? Their labeling leaves something to be desired. From that label I would think that is a 45 watt Radio Spares clone not a Drake 118 clone that belongs in a 50 watt with a SS rectifier.

Yeah according to the MM site, the P45RS is a JTM 45 Radiospares clone... See here:

http://www.mercurymagnetics.com/pages/c ... rshall.htm

Did you get your OT from them too? What model is that?

I knew I was using a PT for a different design. I had that PT in stock for my Plexi Crunch (JTM 45 clone), and Paul told me that some wires would be unused in this circuit. I'll have to wait to hear back from him on which ones.

Jim I would think that 45rs tranny would need to see only kt66 type power tubes? I would guess you want to use el34 tubes in your 50w build? I am not familiar with Mercurys products so I could wrong, please let us know what Paul says about it.. Steve

Steve, the P45RS puts out more B+ voltage (350-0-350 vs 323-0-323 for the G2) than the regular 50w P4550 G2 PT models, which in turn should make it a bit more aggressive sounding, which is why I went with it.

The output tranny I'm using is the PLM050 model which has a different wind to it allowing more even harmonics and sweeter tone. That's where I was heading with this amp.

The P45RS PT works with EL 34's, KT-66's etc just fine, just the usual bias changes/resistors/etc to accommodate the tube used is what you need to change. I've already used these with my JTM 45 clone with EL 34's.

Jim thats great info, I wanted to do the same thing with a 45 build and use el34 tubes ,but the transformer I was using wouldnt work so I scrapped the idea, thanks Jim, cant wait to hear some clips when your build is done.

bluze81 wrote:Jim thats great info, I wanted to do the same thing with a 45 build and use el34 tubes ,but the transformer I was using wouldnt work so I scrapped the idea, thanks Jim, cant wait to hear some clips when your build is done.

Well, probably the best thing is for us to get together and hear it in person when it's done, right? Shoot me an email if you're up for that.

Looks like the two sets of heater wires do have a purpose after all.

Green is for the preamp tube heaters, and the Gray is for the power tube heaters. Green and Gray can be reversed, it doesn't matter which goes where.

http://forum.metroamp.com/viewtopic.php ... highlight=

See Rhinson's post.

I had to know if this was the answer, so I called Mercury Magnetics and they affirmed that one set is for pres and one set is for outputs.

I imagine that this permits a bit more stability for the tubes? Just a beginner here.

The amount of information that is available in the Metro Forums is simply astounding! Finding obscure bits can take some time, though!

You don't need to use both heater wire sets, just one. I went with the green pair. It's the only color that matches up to George's Heyboer wiring. LOL

After I get the 050 PLM installed, and that wiring dialed in, I'll take some pics for George so he can add it to the 50 watt kit stuff.

The only reason I'm doing this is because I had this PT & OT already, and Paul at Mercury informed me it put more volts on the plates than the Heyboer or the P4550T G-2 PT, so it would be a more aggressive tone because of that, which is what I wanted anyway.

I have the PT wiring down, now I have to get the OT wiring cross-referenced, then I can get going on the kit...after I ship 40 speakers, get ready to leave for a week on Saturday, and learn all these songs for the cover band I just joined.

But I'm not busy...

Just got off the phone with Paul at Mercury. The OT Wiring cross - reference from Heyboer 50 w George uses (784-139) to Mercury 050 PLM is:

Heyboer 784-139 Mercury 050 PLM
Brown = White

Red = Brown (This is the Center Tap)

Blue = Red

On the output side it's:

Black = Orange (Common)

Orange = Yellow 4ohm

Yellow = Green 8 ohm

Violet = Gray 16 ohm

You'll all be way ahead of me by the time I get back from Austin, but here's as far as I've gotten on my 50 w build.

Yeah. Well, some of us, but not me. I got the speech. "You can check the part list, but I'm wrapping it for you and it's staying wrapped until Dec. 25th"--that speech. Messing with female operating systems is like messing with an electrical system. Sometimes just not worth it. Double damn!

thousandshirts wrote:Yeah. Well, some of us, but not me. I got the speech. "You can check the part list, but I'm wrapping it for you and it's staying wrapped until Dec. 25th"--that speech. Messing with female operating systems is like messing with an electrical system. Sometimes just not worth it. Double damn!

Well at least you know for certain it will be a Merry Christmas!