first questions on #124 build

[mad_dog]

Ok here are the first of what I'm sure will be many questions.

I have been told to stay true to the original as much as possible however

1. I am guessing that the power supply attached should be ok, as it is a little simpler and parts are easier to source. (however there is a big difference between 300uf and 220uf)

2. Can someone school me a little on the relay power supply. From what I figure it just supplies a regulated voltage to the relays. Can some one suggest the best voltage regulator, the best relay and the best place to source relay boards (I don't really want to etch PCB boards)

3. Do I need the FET circuit or can I just remove it and use standard Hi / Lo inputs or is it worth while including, again I don't really want to etch PCB for the FET

[sergio]

1)Early PS work fine on my #124 amp.
100uF for 50W and 220uF for 100w amp.

2)For voltage supply relays,I use a little trafo 9Vac sec. and voltage regulator 7806. My relays work with 6Vdc.

3)you can omit the Fet circuit but you must place a tail resistor for simulate circuit and run with right voltage.

Sergio

[Bob-I]

2)For voltage supply relays,I use a little trafo 9Vac sec. and voltage regulator 7806. My relays work with 6Vdc.

There are a number of other choices as well. Dumble used a 6V xformer, a voltage doubler and a 7812. You could also use a 12V xformer and a 7812. The 78XX regulators work well.

[David Root]

I use a Hammond 166E12 transformer (12V CT, 150mA), a BR34 bridge rectifier (3A @ 400V), a ST LD1585CV12 12V/5A regulator in the T220 package and two 1,000 uF/25V caps. All (except transformer) mounted on a board 1" x 3". See pic below.

The ST regulator is overkill but I had them, a 7812 is cheaper and just as good for this duty.

You could also use the Hammond 166C12 (12.6V CT), 50mA if space is really at a premium, it still has enough current for two or three relays.

[mad_dog]

Ok I'm looking at RJ's 100w edcor PT as it has the extra 5V 3A tap as I am struggling to find a Filiament PT with a 240v primary (I live in Oz so need export primaries)

could I simply use the same setup as in the Tweaked d'lite layout here
https://tubeamparchive.com/viewtopic.php?t=10255

[mojotom]

I needed to find that same transformer and almost every shop carry the 6V-0-6V (I use 10VA), just use one side only (6V-0).

[Structo]

Sure if your PT has a 5v tap that works great.
That's what I used.

You can build just about any power supply for the relay as it is not super picky about the quality of DC.

I used the 5v tap and a regulated 8v supply with the sensitive Omron relays.

If you don't want to go the pcb route on the relay board you can use perf board or drill out a piece of garolite and put eyelets or turrets on it.
Although it is hard to use those on the relay socket because the pins are so close together.

Ampdoc here sells a very high quality pcb set which includes the relay and PS boards for approx $30.
I bought them and they are very nice.

I used my old PS with his relay boards.

Here are the Mouser part numbers:

Relays 653-G5V-2-H1-DC5 ( these are 5v but you can get any voltage you want for these)

16 pin relay Sockets 575-199316

Diodes 621-1N4007

Here is a schematic of the PS.

The last shot is of the Ampdoc relay boards.
The board is scored at each relay section so it can be broken and used individually or as one relay board as shown.

The power supply parts I used are:

5 – 470uf 25v radial caps – Mouser Part # 140-XRL25V470-RC
2 – 1N4007 Diodes – Mouser Part # 512-1N4007
1 – 8v Regulator – Mouser Part # 511-L7808ABV
1 – TO-220 Heatsink – Mouser Part # 567-274-1AB
1 - .1uf capacitor (not pictured) – Mouser Part # 140-PM2A104K
1 – 4-40 x 3/8” screw and lock nut

[David Root]

Tom, where do you get that green triple relay PCB?

[Structo]

Ampdoc

[Guitarman18]

mad_dog wrote:

1. I am guessing that the power supply attached should be ok, as it is a little simpler and parts are easier to source.

On my most recent build, I used Vibrolux iron, which put out @375v. This gave me 491v on B+2 node!!!

My original power supply was the non precision type, as you have shown above, but I ended up having to upgrade it to precision PS. I just didn't feel comfortable with the voltages that close to the 500v cap limit.

So it is worth knowing what your PT is going to be putting out when making your decision.

Maybe this type of situation was one of the reasons HAD adopted the precision power supply in later builds?

Hope this helps.

Cheers,

Paul.

[mad_dog]

Ok I think i'm getting my head into this now.

I think I am gonna spend some time looking over the preamp layout + schematic to see if I have any more questions. From what I gather getting the voltages right is pretty important on these amps

[Structo]

Yes the voltages on the preamp tubes and PI are very important to get the D tone.

On my D'lite the PT has 325-0-45-325 300ma
The 45v tap is the bias tap.

The 6.3v tap is 6A and the 5v tap is 3A.

If you get a similar spec'd PT then you can use the dropping string shown on the schematics.
If your amp is built without the FET preamp, then you add a 150K resistor at the end of the dropping string to simulate the FET load.