Gibson Ranger GA20-T Rebuild

[Leo_Gnardo]

Thanks Greg... Yes, that is helpful.

I'm going to creat my shopping list soon. I guess the questions I have center around the types of caps I should get. I see the bumble bees and the ones I call "the bananas." Based on the experience of others, i am wondering if Orange drops would work ok in some spots but axials in others.

Coming off the power supply, we have the two 10k resistors. One measures at 10.5k and the other at 9.5k. So I will strat there and continue on.

Tom

OD's will work fine for all applications, but my preference is Mallory 150. Antique has some even cheaper film caps which are OK. I always opt for 600 or 630V ratings. No point in buying bumble bees. New ones are merely film caps encased in plastic and painted with stripes and an absurd price tag. Old ones, who knows whether they work or not no matter what the seller claims. Either way, a lot of $$$. Your 10K resistors are close enough for rock'n'roll. If you choose to replace, you can get spendy carbon comps, but I use 2 watt metal oxide resistors, cheap & I never had a failure.

[52 Bill]

I'm going to creat my shopping list soon.

Tom, are you planning on a shotgun replacement of everything in the amp or are you going to power up the amp first and see where you are at before making repairs?

[TomCarlos]

I will change out the electrolytics and any resistors that appear to be way out of whack. The initial power on will be with a variac and bulb limiter. I'd hope to see a signal at the output. From there, it will probably be a step by step. But I think my friend would be ok if we replaced all the caps.

[soundmasterg]

I would say that due the difficulty of replacing the caps on this amp without having to take the whole board out, then you should connect each signal cap to a DC voltage like 300V and see how much they leak DC. Most likely all of them are bad except perhaps the domino mica cap, and should be replaced along with the electrolytics. I used M150's in the one my brother has. They fit well and sound great. I didn't use any orange drops....the usual orange drops that people tend to get are the 715P which are polypropylene and are not going to sound the same as the polyester and paper or paper-in-oil caps that were in that amp when new. Polyester caps like the M150's, Sozos, the AES cheap yellow polyesters, etc will sound much closer to original than anything else you might get. The PS series Orange Drops are polyester but they are film/foil type of construction so they are huge, and they are also radial caps. The amp was made to use axial caps so they will fit better.

For resistors, the usual ones that need replacement are the ones in the power supply and any plate resistors in the preamp as they tend to get noisy and crackle.

Greg

[TomCarlos]

Thanks Greg....

I appreciate the advice and that from Leo. I'll have some time this weekend and will order some parts for the amp. I'm looking forward to the first slow power up and seeing this amp come alive!

I'll also post some photos and notes of my work along the way. One thing I want to point out are exceptions to the belief of "this is an exact replacement...." For example, the Power Transformer windings (and voltages) might be an exact replacement but to mount the unit, you need to drill a couple holes in the chassis. Otherwise, the PT brackets do not align with existing chassis holes- stuff like that.

[52 Bill]

One thing I want to point out are exceptions to the belief of "this is an exact replacement...." For example, the Power Transformer windings (and voltages) might be an exact replacement but to mount the unit, you need to drill a couple holes in the chassis. Otherwise, the PT brackets do not align with existing chassis holes- stuff like that.

I had the same experience with one their output transformers. A friend asked me to look at his mid 60s Dual Showman. The OT was shorted, etc. He wanted a MM so he ordered one and it didn't physically match up either.

I can never find any real information on their transformers, like dimensions or elec. specs. I guess that's part of the mystery or smoke and mirrors.

[Leo_Gnardo]

I'll also post some photos and notes of my work along the way. One thing I want to point out are exceptions to the belief of "this is an exact replacement...." For example, the Power Transformer windings (and voltages) might be an exact replacement but to mount the unit, you need to drill a couple holes in the chassis. Otherwise, the PT brackets do not align with existing chassis holes- stuff like that.

Gibson's caps stashed "behind the board" - I've managed to fish them out when necessary without having to pry the whole board out. A good flashlight & dental mirror help find where they are, then snip leads & unsolder the stub leads from solder tags. What a hassle, but a little easier than prying the board out, especially when board mounting post screws are hidden under transformers. I put the replacement caps on the board side, no more hidden surprises.

I've always been able to source replacement transformers from Antique/CE or Magic Parts (Ruby) or Mojo. If they don't fit exactly, gotta drill holes, at least I'm not paying a super-premium price like Mercury. Some seat of the pants guesswork may be involved. Mostly I look at whatever Fender amp resembles the amp that needs the iron, and get the Fender part. Failing that, theres' a good selection from Hammond. Another good spot to hunt for iron is Hoffman. So far I haven't dealt directly with Heyboer but they do have an excellent reputation and prices are reasonable. Weber carries some Heyboers, and I've built kit amps with transformers sourced from them, they work and sound just fine.

[Enzo]

If a film cap is on the back side, I usually snip the leads where they curl around the board edge, then fish the cap carcass out from under. I just munt the new cap on top, stacked on a resistor if need be.

[Chuck H]

If a film cap is on the back side, I usually snip the leads where they curl around the board edge, then fish the cap carcass out from under. I just munt the new cap on top, stacked on a resistor if need be.

I catch some flak here whenever I suggest anything like this. When Enzo does it, it's "clever".

[Enzo]

It's because of my good looks...

[TomCarlos]

Thanks mates... I am building up my shopping list and looking at the various caps in this circuit.

I see the bananas, the bumble bees, and then there is that big white CD .25uf cap (400v) that hangs off a grid from the 5879 tube (the second input circuit). Anyone have any ideas why this is a "different" type of cap? Is it some type of electrolytic with a polarity and that is the difference? Is that why I see a black band around one end of the cap (which happens to tie to ground)?

[Leo_Gnardo]

I see the bananas, the bumble bees, and then there is that big white CD .25uf cap (400v) that hangs off a grid from the 5879 tube (the second input circuit). Anyone have any ideas why this is a "different" type of cap? Is it some type of electrolytic with a polarity and that is the difference? Is that why I see a black band around one end of the cap (which happens to tie to ground)?

Looks like a film cap, not electrolytic. I'll bet it goes to one of the 5879 grids, likely g2, not the control grid. Black band probably indicates "outside foil."

[TomCarlos]

Thanks Leo.... I'll take a careful look at the caps when I get this. This one from tubesandmore doesn't have a band around it.

[Enzo]

Look at the other caps in the amp. They are 0.02, 0.005, 0.01, 0.05uf. Now look at your 0.25, it is larger because it has 10 or 20 times the value or more. it is bigger because it is a larger cap value, that is all. The band means outside foil, and really, though people will debate it forever on the internet, it won't matter which end is which when you replace it. it is just another film cap.

In the circuit, this cap is a screen bypass cap for that 5879. it is enough, it doesn't have to be a larger electrolytic.

[Leo_Gnardo]

Thanks Leo.... I'll take a careful look at the caps when I get this. This one from tubesandmore doesn't have a band around it.

As Enzo said, no worries about outside foil. Plus "close enough" value will work just fine, 0.22 or 0.33 uF film cap 400V. That cap's not going to see more than 300V max in its application. (Sunday morning back of the envelope guesstimate.)