REDD 47 PCB

[michal_k]

Not sure yet, I've started drawing this PCB just as an exercise, but now, when more transformer options have been posted, I feel tempted to try it. If there are enough people interested to make a pcb run in reasonable prices(around 10pcs at least I guess) then I can order some.

Edit:
Changed ecc88 plate resistor for a 5W one, moved cathode cap further away from the tube. 240R resistor should be mounted on the gain pot's legs and wired with shielded wire to leftmost two ins in the X1 terminal. Do whatever steps you want with the gain switch and hook it up with shielded wire to rightmost part of X1. I'll look into PSU now.

 

[monkeyxx]

I might be interested in a few channels.  I'm not totally hell bent on point to point.  Mainly I just didn't want to pay the Drip price.

If I were to build several channels like in the turret board layout each with their own power section, would I need a separate power transformer for each one?  Say for two channels in one 2RU rack.  Or my other question might be, how many channels could one power section, as per the original schematic, capably power?

 

[michal_k]

Not sure what you mean by power section. If you refer to the part in original schematic my advice would be to not use it at all. Much better solution would be to use modern psu for way better noise performance. Also, a good power supply with low output impedance can easily power two channels of this pre without any negative effects like crosstalk. What I would be more worried about when building two channels in one box is heat as pointed before by My3gger.

 

[My3gger]

Thanks for the tips, I'll change ecc88 plate resistor for a 5W type. As for the capacitors near tubes, I've intended to use jj-electronics tube type caps that have a bit higher temperature tolerance. I guess I'm gonna have to build it to see how hot the caps get. For now, here's grounding scheme and full wiring. As always, I'm looking forward to your comments.

Yes, build it and put thermometer probe inside rack, while other gear and preamp are on for several hours. From datasheet information i calculated, that some of better new lytic caps would survive pretty high temperatures for very long time. When i compare JJ to some Epcos lytics former seem to have much longer life, but they are of course radial snap-in. In one case Mundorf MCap's outer foil started to unroll when it was ~ 3cm from 8k2 made of 2 and 3 w resistors. I can't find datasheets for some of "audiophile" foil caps. Wima has then and they are radial too.
Another problem, beside lifted traces from heat, was more lifted traces from plugging and unplugging tubes. For simple circuits like this one i find L brackets with tagstrip/veroboard/pcb durable and easy to make solutions. I wonder what will happen with Drip's pcbs with lots of hot tubes, resistors and also transformers on them. Lots of heat and weight even for open chasis.

 

[Mike Cleaver]

RCA and other radio control room console makers were using printed circuit boards in the '50s, also with plenty of hot tubes usually running 24/7.
The tube sockets were mounted on the pc boards.
The only problem I ever saw with traces lifting was when smoking was permitted in control rooms. 
The tar, nicotine and other crap in cigarette smoke formed a corrosive that caused traces to lift.
Also, the DRIP boards are VERY thick and very well made.
I don't think trace lifting and failure will be much of an issue.

 

[alexc]

Redd47s don't get that hot - even with 2 in a 2U no probs. At least, in the case where the is not excessive heat dissipated from any regulators.

The 5W resistor gets a little warm - mount it standing a bit higher off the pcb.
The au7 gets a little warm but not much.

Not even close to being a problem for lifting tracks or anything else.

As long as the rack enclosure has ventilation slots on top and better still, sides - all good.

If you are really conservative, leave a 1RU space on top when racked up. Or use a 3RU enclosure.

I would regard it as being a quite cool running dual 2RU unit.

To categorically state that 2 of these is a 2RU rack is a fault waiting to happen is far too dramatic, imho. 

 

[Gearsix]

I have read that the low frequency cut is obtained with an 1,8uF capacitors in series with the input line before the transformer. Someone has tried it?

 

[buildafriend]

your coupling capacitors can set your cutoff frequency

check out the capacitive reactance formula

 

[buildafriend]

I was looking for the 8.2k resistor and I found one but I'm questioning if this one http://www.mouser.com/ProductDetail/Vishay-Dale/RS0058K200FB12/?qs=sGAEpiMZZMukHu%252bjC5l7YSE%252bBpkuXBrKkE80lG%2fthfk%3d might be a better option. It seems to have what might be a pretty large footprint for the orange 86 board.

 

[michal_k]

you can always mount it vertically or a bit above the pcb and bend leds inwards. Either way will only improve heat disspation.