Recycling old Gibbs/Accutroincs tanks

[frankleslie]

Ur welcome Phil, by the way the minus on the rectifier should also be connected to ground. Forgot that on the schematic. I use a Bell & Howell speaker from 1952, with this amp. Sounds very bright but in a pleasent way, as I imagine the old American amps would have sounded like. The 6SJ7, is very microphonic so avoid using it in a combo.

[Phil_S]

I had read the schematic as if the bottom line was a ground buss. Ground symbol or not, it was implied quite adequately. What else would you do with it? I am assuming you are using a packaged rectifier, not loose 1N4007's or similar. All this goes on a PC board?

Now I'm trying to understand how to mount and build this gizmo. It looks like I need PC boards with sockets, etc. I'm thinking small breadboards. I don't believe I've got the inclination to actually get into what's needed to etch a board. I'll tinker with layout as time permits. The sand itself sure is dirt cheap!

Can I assume, as long as I isolate the two circuits (power supply; reverb) they can live on the same board?

Approximately what size board? I don't have a sense of scale. Most of this stuff looks quite small compared to what we use for tube amps.

[frankleslie]

I used a bridge rectifier, small one, but 1N4001-7 can of course be used. I put the parts on a stripboard/veroboard/prototyping board and tried to make it as compact as possible and using an 8-pin socket for the IC, in case I need to replace it. I used metal film resistors 1/4W and PCB mounting (radial) capacitors of 100Volts or more, MKT or MKP type. I just used the smallest I had lying around. Get a board of standard size, maybe 10 by 15 cm, figure out where everything has to go (this takes time) and cut to the size that you want. Don't forget to leave room for mounting holes and the regulator ICs should have a small heatsink on them, anchored to the board itself for stability. You can put it all on one board, no problem. Place the board as far away from power transformers as possible. I mounted the Belton brick on the back of the chassis, on the outside, with the connector pins going through the chassis in cut outs. I have no pictures at this stage as it is in use by a friend. Anyway good luck!

[Phil_S]

OK then, I should be able to do this. I just took a close look at the BTDR-2, and realized how small it is. I saw thinking like a 3/x5 card. It turns out it's roughly like maybe a pack of matches! I was really quite surprised about that. Outside of the chassis? I can try that. Thanks again.

[Phil_S]

I'm a frikin' newbie with sand! For that op amp, do I need T072-CN or T072-CP? Does it matter? I have a T072CN on order. I ordered from a surplus place and this is what they had. Then I found out there is the other kind. Can I use it? No big deal if I can't. It was only 35¢.

In case it makes any difference, I'll be supplying power from the 5V heather winding through a doubler. I figure it will give me 5.5V *2.8 = ~15VDC. I can tap it for + or - voltage to the 7805 and 7815 voltage regulators.

Thanks for any help you can offer.

[TUBEDUDE]

Phil,
The last characters designate the case, ceramic plastic, in line or dual in line pins etc.
the regulators need a little voltage over their output to operate correctly. IIRC the 78 series needs 1.5V over. I think the MAX series regulators require less.

[Phil_S]

Phil,
The last characters designate the case, ceramic plastic, in line or dual in line pins etc.
the regulators need a little voltage over their output to operate correctly. IIRC the 78 series needs 1.5V over. I think the MAX series regulators require less.

So, it's good news and bad news. The TL072 is for a TO-220 form factor, so I bought the correct heat sink and thermal insulator -- all of these were dirt cheap, too.

On the input voltage for the 15V regulator, I might be able to squeeze by with a large enough cap. The 5V winding is on an old PT. I figure it will give me about 107-108% of its rating. Also, it is a 3A winding, so the meager 100mA or so that needs to be provided won't be pulling down voltage. I can model this in Duncan's PSU to see if I'll be able to skate on this, and then, since I've still got the PT on the breadboard, I can do an actual load-based simulation to see if it is in line with what the PSU software predicts. If it's not working, I'll have to find plan B.

I could try a voltage tripler? What happens when I show 23VDC to a 7815? And is that too much for the 7805?

Thanks.

[ToneMerc]

What happens when I show 23VDC to a 7815? And is that too much for the 7805?

Max input voltage to the 78xx series is about 37-38 volts, but keep in mind that any input beyond a few volts higher than the target voltage is wasted and is dissipated as heat. Thus, you will need a good heat sink.

TM

[Phil_S]

TM, thanks for the pointer. I have on order what seems to be the usual and customary heatsink for the TO-220 package. I have some big ones that used to have transistors on them and I imagine I could hack them down to half size and still have a decent hunk of metal.

I've been snow bound all day. Honey do's minimized bench time. The PT 5V @ 3A winding puts out 6.03VAC unloaded. I am guessing the load of less than 100mA will not pull the voltage down very much, meaning a doubler will yield 6 * 2.88 = 16.8VDC. Allowing for a minor loss, 16.5VDC looks like it can be achieved. If not, I'll got to a tripler and the problem will be solved. I'll keep in mind maybe I need a heftier heat sink.

I'm just glad I don't need to add another transformer. As it is, I think the chassis is going to be crowded.

[TUBEDUDE]

TO 220 for an opamp? I didn't know a TL072 was offered in a TO220. Are your regulators in TO220 or TO3? If TO220, they are easy to heatsink to the chassis with an elastomer insulator.

[Phil_S]

No, I got confused. The 7805 and 7815 voltage regulators are TO-220. The TL072 op amp is an 8 pin DIP that goes into a socket. Please excuse me, all this sand is very new to me.