50w Build started, have a couple of questions

Get support and show off your MetroAmp 50 Watt kit builds.

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Explorerman
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50w Build started, have a couple of questions

Post by Explorerman » Sat Jun 04, 2022 9:08 pm

Hi, I’ve started my 50w build - it’s a 1987 bright channel switchable to 2204. Its my third amp build but I might use this thread to ask some questions as I go.

- in the below pics (hopefully u can see them? It wont let me upload photos??) I’ve left a little loop on each of the wires on the under side of the board, is this ok? Or should I just have the wires come straight out from the board?

- what is the easiest: populating the board with components before or after installing the board into the chassis? My last two builds the populated the board first, then installed it, had no issues. However, the Metroamp instructions has it as installing the Howard first then populating with components.

https://www.dropbox.com/s/86pe21876rjm5 ... .HEIC?dl=0

https://www.dropbox.com/s/aiq1h8qxnu53 ... .HEIC?dl=0

Any help greatly appreciated, thanks.

danman
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Re: 50w Build started, have a couple of questions

Post by danman » Mon Jun 06, 2022 5:56 pm

After the forum was hacked several years ago, the new software will no longer allow direct photo uploads for safety reasons. They must be hosted on an image site and then linked to in your thread.

I prefer to solder all of my wires to the base of the turrets first and then load my components into the top of the turrets. Soldering the wires on first allows me to achieve a nice solder dome on top of the turrets when soldering my components in. After everything is loaded and soldered onto the board, I will fold the wires back over the top of the board to make it easier to load into the chassis. Once bolted into the chassis, I will then trim each wire one at a time and solder it into the circuit.

Your little extra loop of wire should be ok.

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Re: 50w Build started, have a couple of questions

Post by Explorerman » Mon Jun 06, 2022 6:24 pm

Thanks danman! Great to know.

Also, is it best practice to have the pre amp 32/32 filter resting on the board or raised up a bit held by it legs? I’m going to struggle to get the 10k resistor that runs along side it to reach across between the turrets.

What is the typical length of the section of component legs that goes into the top of the turret hole?

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Re: 50w Build started, have a couple of questions

Post by danman » Tue Jun 07, 2022 6:08 pm

I normally like to lay heavy items like that capacitor flat on the board to take the stress off of the wire leads but in this situation, you do need to make room for the 10k resistor that lays beside it. In my 50 watt build, I cut a small piece of foam and glued it to the board right under the capacitor. This allowed me to rest the cap on the foam for support yet still leave room for the resistor to lay under the cap. The foam was only about 3/8" wide and 3/8" to 1/2" tall. Just big enough to give support to the cap but still small enough to be hidden from sight. If you don't have any foam, a small piece of plastic or wood will also work.

I normally leave about a 1/4" of component lead folded down into the turret's hole. You can go longer but keep them short enough that they don't poke out from the bottom of the board. It would be very easy to damage a wire passing under the board if those component leads were hanging down too far below the bottom of the board.

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Re: 50w Build started, have a couple of questions

Post by Explorerman » Sun Jun 12, 2022 3:46 am

I like the idea of glueing some foam to the board under the pre amp filter cap (I might need to do this with the V2a cathode 0.68uf cap as well - it’s quite tight with the turret posts compared to pics of the other type of board in the instructions).

Questions - how hot does that 10k resistor that runs alongside the pre amp filter cap get? As long as it is safe to sit next to the piece of foam - see below pics.

Also, see that 10k resistor in the below pic that just reaches between the posts, I’ll only manage about 90 degrees wrap, do you think this is sufficient or should I attaché another piece of conductor to it? (It’ll be hidden from the pre-amp filter above it anyway).

Does anything else in this pic look like it might give me issues? (Just want to get it right First time as I don’t like re-work). Cheers!

https://www.dropbox.com/s/7nln92z2fo022 ... .HEIC?dl=0

https://www.dropbox.com/s/kuf1kyz9vwocs ... .HEIC?dl=0

https://www.dropbox.com/s/bjk5c18hc8sil ... .HEIC?dl=0

https://www.dropbox.com/s/l5l00wskcvek4 ... 3.jpg?dl=0

https://www.dropbox.com/s/txv9zxgfwwsx5 ... .HEIC?dl=0

https://www.dropbox.com/s/yicdek5ly6g33 ... 5.jpg?dl=0

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Re: 50w Build started, have a couple of questions

Post by danman » Sun Jun 12, 2022 6:34 pm

The current flow through that 10k preamp decoupling resistor is so small that the resistor barely gets warm. As for the resistor with the short leads, I ran into the same problem also when building my 50 watter. I ended up doing exactly as you did and it has never given me any troubles. As long as your solder joint is good, the resistor will never come loose under normal conditions. Some of the turret spacings are so wide that modern resistors simply aren't long enough. You will notice in vintage amps that Marshall also ran into this problem in one or two spots so they used 1 watt Allen Bradley carbon comp resistors because of their extra lead length. Everything else looks good to me also.

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Re: 50w Build started, have a couple of questions

Post by Explorerman » Sun Jun 12, 2022 6:53 pm

danman wrote:
Sun Jun 12, 2022 6:34 pm
The current flow through that 10k preamp decoupling resistor is so small that the resistor barely gets warm. As for the resistor with the short leads, I ran into the same problem also when building my 50 watter. I ended up doing exactly as you did and it has never given me any troubles. As long as your solder joint is good, the resistor will never come loose under normal conditions. Some of the turret spacings are so wide that modern resistors simply aren't long enough. You will notice in vintage amps that Marshall also ran into this problem in one or two spots so they used 1 watt Allen Bradley carbon comp resistors because of their extra lead length. Everything else looks good to me also.
Thanks For verifying. Good to know that resistor won’t get hot as well (I’d hate to melt that foam). With regards to the method of installing the 10k - which method were you referring to as the one you used - the 90 degree wrap on the post or joining on some conductor?

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Re: 50w Build started, have a couple of questions

Post by danman » Mon Jun 13, 2022 6:01 pm

I was trying to say that there is no need to add additional lead length to the resistor if you feel your solder joints are solid. I have a couple resistors in my amp that didn't get a good wrap on the turret but they are still holding just fine.

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Re: 50w Build started, have a couple of questions

Post by Explorerman » Mon Jun 13, 2022 11:01 pm

:thumbsup: Ah no problem, I’m confident I’ll be able to get a good solid solder connection, I’ll run with that idea, cheers.

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Re: 50w Build started, have a couple of questions

Post by Explorerman » Mon Jun 20, 2022 4:25 am

Another question: just regarding the OT primary red and white leads, am I guaranteed that with the red going to V4 and white to V5 that they will be in phase? (I’m using a APD Heyboer OT). I’m only asking because if I wire it as per the instructions and it ends up out of phase the red wire won’t be long enough to reach V5 if I need to swap (not the end of the world I know, but would just prefer not to join wires if I can help it).

Also, do you just run the choke and OT wires straight into the grommet/hole then to their destination without any loop/slack (this what the instructions seem to have) or is it ok to leave a little slack for some extra length if ever needed? Or will doing so potentially induce noise?

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Re: 50w Build started, have a couple of questions

Post by danman » Mon Jun 20, 2022 6:41 pm

There is never any guarantee that the OT will be in phase. Always leave them extra long until the very first power up. If there is no squeal, then you can trim them down to length. If they do squeal, reverse them and trim them to length. Normally they squeal as soon as the tubes warm up but I have had one or two builds that did not squeal immediately but the amp would act funny whenever I started playing through it. After several hours of troubleshooting, I reversed the wires and the problem went away. Even of the amp doesn't squeal right away, play through it for a bit before deciding to trim them to their final length. If you have already trimmed them and they are too short to reverse, you can switch the wires leading from the phase inverter to the grid (pin 5) of the power tube sockets. This serves the same purpose as switching the OT primary wires.

I normally leave just enough slack in the choke and OT wires to allow me to unsolder, trim and reconnect them if I ever need to perform any service work in the future. A little extra slack won't hurt you but you don't want to much extra wire in the amp. The AC power supply wiring and filament wires should always be kept as short as possible because they are the noisiest wires in the amp.

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Re: 50w Build started, have a couple of questions

Post by Explorerman » Mon Jun 27, 2022 4:51 pm

Thanks Danman sounds good.

I’ve been waiting for the past 6-9 months for a APD Heyboer PT, still no stock. How much longer till these are available again? I’m considering a Hammond PT290GZ, specs say secondary voltage of 345-0-345, will this give the same ideal B+ that the Heyboer gets? Or would I be better off going with Mercury?

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Re: 50w Build started, have a couple of questions

Post by danman » Mon Jun 27, 2022 5:56 pm

Since Classictone closed, Heyboer has picked up the slack for many of the boutique companies. They seem to be inundated with orders and are winding and shipping to there larger customers first. It's great that they managed to stay in business over the last two years but it does suck for us little guys who just need one or two transformers a year.

I know that my PT that I purchased from Classictone for my 50 watt build several years ago was rated at 345-0-345 @150ma, 6.3v @ 5ma. That gave me a final B+ voltage of 420-430vdc at a bias of 70% or so. This is pretty much the standard spec so any PT that supplies you with something close will work just fine. Some folks like a slightly higher B+ of 450-460vdc for a slightly punchier and tighter sound while others prefer the lower B+ of the late 70's amps which came in around 370-380vdc. These were a bit softer and browner sounding than the higher B+ amps of the 60's and eraly 70's. Choosing a PT with a higher "ma" rating on the secondary will leave you with a stiffer feeling amp that doesn't break up as easily. Some builder will go as high as 250ma on the secondary for a stiffer feeling amp but the classic Plexi sound was with a lower rating of 150ma or so. I couldn't find any info on the Hammond PT290GZ but if it's close to the specs of the Classictone it will work just fine. Just make sure that you have at least 5ma on the 6.3v winding for the filaments. I have used Hammond iron in several of my builds and highly recommend them. Edcor is another great company that has many to choose from but there is normally a 2-3 month wait time for their iron. Here is another company that I have used several times and have always been happy with his service and products.

https://www.musicalpowersupplies.com/products/

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Re: 50w Build started, have a couple of questions

Post by Explorerman » Mon Jun 27, 2022 9:42 pm

That is great info to know! The Hammond PT is 150mA.

https://www.dropbox.com/s/gz27sxgoynq4h ... 7.PNG?dl=0

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Re: 50w Build started, have a couple of questions

Post by danman » Tue Jun 28, 2022 6:26 pm

That should work just fine.

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