Metropoulos Forum

Ok, I am gearing up for a NOS component (Iskra & Piher resistors, Mustard & dogbone caps etc) '69 era 100 watt superlead build. I have a Modulus blank, perforated phenolic board, but am aware that these can absorb moisture unless "sealed" however I am a complete dummy with regard to sealing boards. If anyone can offer advice on what type of sealer to use & tips on application of the sealer it would be greatly appreciated. I would like the board to retain a stock look after sealing. Thanks in advance. Cheers

I wasn't aware that these boards had that issue but I have had very little experience with them. I know the old boards that Fender used were notorious for becoming conductive over time. Hopefully Neikeel or one of the other knowledgeable members will see this and chime in.

The Modulous boards I used in the past (bought maybe 14 months ago) are not the best grade material out there for vintage style boards. The Modulous stuff I had ran about 60ma to 100ma but good Electrical grade will have Zero conductivity.

I dont think you can seal the boards.. just store is a dry place.

The boards are ok for a personal build I guess but I would never a amp to someone with Modulous boards.

Thanks for the input guys. Speaking with Neikeel a couple months back (pm), he confirmed that the Modulus phenolic boards leak but can be sealed, but as I said, I'm a complete dummy when it comes to sealing a board. I do have a (dark brown/almost black) perforated FR4 G10 board that I can use (I turret my own boards), but it doesn't look as authentic. Being as this is a NOS component build, I want it to perform as best as possible, so don't want the board to leak current. I have two or more of "most" components so can choose those that meter closest to spec. Iron is m****n, transformer brackets & choke Classictone (I'm still deciding 3 or 5 Henry, input welcome), headcab, chassis, hardware etc Valvestorm. The only thing I'm still searching for is the RS 0.22uf/1000v rectifier snubber caps. I do have two NOS (light blue) LCR axial types to use for this, input on their suitability also welcome. Hopefully Neikeel will drop by & offer advice, he is extremely knowledgeable on these amps & also one hell of a nice guy. Cheers

Edit; Just out of interest, I recently (3months ago) did a NOS Iskra (1 megs are Piher), mustards & RS silver Mica rebuild of my tube rectified, '68 spec 50 Watter. That has one of the Brian Haberman boards in it, Marstran iron. Valve compliment is all NOS/NIB. A 7 notch Mullard F32 GZ34, a duet of XF2 single halo Mullards EL34's biased to 60%, a Brimar CV4004 in V3 (plate differential voltage 7.8v, a tad high but still ballpark), Brimar CV4004 in V2 & a 163 series Mullard in V1. Sounds glorious. It will get a Mullard 163 series in V3. Hopefully this upcoming build will be in the same league. Cheers

I'm not sure what sealed means. You would have to isolate the turrets from the board.

Maybe we can seal the drilled holes with something that will isolate the turrets from board?

Hi RockinRocket, Neikeel mentioned (pm) possibly using a general purpose sealant on the board. Hopefully he will drop by & offer further insight into what "type" of sealant etc. I do have circuit board lacquer but this would be very noticeable, not an authentic look. You mentioned seeing leakage currents of 60~100mA, do you live in a moist or humid area? Where I currently live here in Oz it is an extremely dry & arid area, but, as I plan on using the amp it will see use in coastal & tropical areas at times.
As I have extra length of the board I could maybe try spraying a test piece with well thinned clear enamel to seal it. Thoughts???
Cheers

I personally would just find better electrical grade boards than go through the trouble.


I don't think humidity has to do with the Modulous boards. Its just not the best type of board and might even be general purpose phenolic. I have the stock code sticker that was left on one of the boards but could not trace it to anything.

Maybe they are selling different stuff now but when you drill into the modulous stuff it should not come out looking like paper cardboard. If it does there is better stuff out there.

Thanks for the heads up. I will try drilling into a bit of the board. If it comes out looking as you describe I will use the darker coloured FR4 G10 board, unless you know of a source for decent perforated phenolic. Pity Chris M****n doesn't have board material at the moment (I enquired when ordering the transformers). Cheers

I talked to the seller of modulous boards as I know who he is on Ampgarage.

He said he's only had one report of conductivity reported in 2015. Believes the user used cleaner to remove flux that lead to conductivity. Kindly offered me a refund on the boards I purchased but its been so long I feel no need.

Modulous boards are the lowest grade boards in its class. "SRBP Grade P1". These are Low tension boards but he says this is what they are made for. I disagree.

Here's a data sheet I found for this class board.
http://www.bakelitesheets.com/pdf/P1.pdf

"have excellent Mechanical Properties and can withstand low tension Electrical applications under non humid"

Sorry 400v + DC voltage should not simply "withstand low tension" It needs to withstand.

Thanks for the info on the Modulus phenolic material. I will be using the dark brown FR4 G10 board.
My Valvestorm order has arrived this last Monday & the M****n transformers are on the way so the build will begin in about 2 weeks. Cheers

Just buy a new board. I have some

axeman wrote: ↑

Thu Mar 07, 2019 3:50 pm

Just buy a new board. I have some

whattaya got.

Thanks for the heads-up on the boards Axeman, very much appreciated. Do you have the fully perforated boards? If so I would be interested in one for sure. Thanks again. Cheers

email me Axeman6@msn.com