Rack stuff

[M Fowler]

I'm still building, hot rodding amps and repairing way too many amps and even my brother's radio.

I had some Hot Rod Plexi preamps built and I'm starting on building a JCM800 rack preamps and some kind of clean Fender preamp after that.

I run the preamps into my Synergy 50w rack tube amp into several different cabs 4x12 Marshall and 212 Avatar.

Mark

Fowler HRP preamp rack 2 (2).jpg

[M Fowler]

On the power supply section for JCM800 preamp build I'm using Hammond 229B230 power transformer and 229A12 filament transformer.

I was thinking perhaps I didn't need the filament transformer could I have just created a 12v regulated 7812 supply off the main power transformer or found on that had both in one small flat pack unit.
The rack is only 1u so not much room to use Reverb power transformer, in a 2u rack I sure could do that.

https://www.hammfg.com/files/parts/pdf/229B230.pdf

Mark

[sluckey]

You can't power the filaments with that PT. Maybe you can find another low profile PT that has a HT and separate filament winding.

[martin manning]

What kind and how many tubes?

[Stevem]

I would preamp wise stay away from running but the first preamp tube on DC.
It take a huge amount of current when even just 3 preamp tubes are being fired up, in fact on a modest gain build I think I would sooner prefer to just bias up the whole heater string!

[M Fowler]

Thanks for the replies guys I appreciate that.

I'm using Hammond 229A12 which has 6.3v or 12v secondary winding but I was curious as to other options.

So I am using Hammond 229B230 to power two 12Ax7's as in a JCM800 preamp
and Hammond 229A12 for filament supply.

I will let you know how it goes after I receive my faceplate, drill holes, make tone board and then power supply board/filter cap section.

Dropping string will be determined later as to adjustment.

Mark

[didit]

Hello --

Perhaps there's a solution in PDF data sheet for Recom AC "line" to low voltage DC converter?

For ~$10 you get enough 12V DC power to heat up a pair of 12AX7s. If well-regulated 12.6V is desired get their 15V device and put an adjustable low-dropout analog DC-DC regulator on it's output.

Best .. Ian

[M Fowler]

I'm building a JCM800 rack preamp using the Hammond 229B230 power transformer and 229A12 filament transformer.

I will be using two 12ax7 tubes which these transformers can handle easily.

OK my question is how do I know when to use full wave bridge rectifier verses full wave. The data sheet states 230v CT @ 50ma or 115v @ 100mA
I want 230v secondary I think rectified and into filter cap. Wiring sheet shows secondary series connection of 5 & 8 connected together and the two wires 7 & 6 = 230v which seems to me would be full wave bridge circuit.

Mark

https://www.hammfg.com/files/parts/pdf/229B230.pdf

[martin manning]

Correct. If you are using a stacked reservoir, you can connect the CT (5 & 8) to the middle of that. Don't be surprised if you get a high unloaded voltage, ~400 or so.

[sluckey]

OK my question is how do I know when to use full wave bridge rectifier verses full wave. The data sheet states 230v CT @ 50ma or 115v @ 100mA

A 230VAC with center tap will give you 325VDC unloaded with a FWB (CT is not used). It will only give half that much with a 2 diode FW using the center tap connected to ground.

[M Fowler]

Martin and Steve, thanks for your info I was going to rig up a test and see what I got but not now.

Mark

[M Fowler]

No gut shots yet but there will be as work progresses.

For now you can look at the outside of the JCM800 with it's new panel from Juicy Amps.
Next time I will increase the height of the panel so we can get numbers on it, live and learn.

The Hot Rod Plexi was made for me and sound great.

Mark

JCM800 preamp.jpg

[martin manning]

Looks great!

[JD0x0]

Any gut pics you're willing to share? I'm curious how the tubes are mounted.

[MakerDP]

A little late adding transformer suggestions, but have you considered this replacement for a 6G15 reverb unit?

https://www.tubesandmore.com/products/t ... one-reverb

Very cool designs by the way!