RCA 480060 replacement

[Jerry]

I've got an Acoustic bass amp witha couple of blown output transistors.
They say RCA480060. Anyone have a recommendation for a modern replacement? Thanks for your help.

[Amp Kat]

How old is this thing ? That number didn't pop up but Enzo gave me a sheet awhile back that had someof theses old cross reference numbers but it's at the shop so you'll most likely have to wait on the master as he may have it. They have a few others here that may knowe but this is more of a tube site then transistor with the exception of a few. I called Mouser and they didn't list it either using the RCA and just 480060.

[Enzo]

That is an Acoustic part number, not RCA's. It just says TO3 110v power transistor.

WHat amp you got, an how many output xstrs? I would just replace all of them with MJ15003 or MJ15024 and be done with it.

[Jerry]

The amp is an Acoustic 320,it's got 2 banks of 4 transistors all of them are the same part#.

[Enzo]

OK, four on the high side and four on the low side, voltage-wise. It is important that all four high siders be the same type and all four low siders be the same type. The high and low can be different types as long as they are roughly similar. (solid state amps are great that way.)

How many bad transistors are there? REmove them. For test purpose, the amp will run - at reduced power output - on as little as one power transistor per side. Just enough to verify that it operates.

Allied sells MJ15003 for $3.63 each. Allied Stk#: 568-1003 And they have 400 and some in stock, so they won't run out soon. So the whole pile of them could be replaced for about $30. If there are only a couple bad ones, replace some from the other side so that one side has four good originals. Now replace all four of the other side with something like the MJ15003. Save the leftover good old ones for future repairs.

You don't want to mix types on one side, because they won't share current well. The odd one will either hog current end try to do it all, or it will not turn on with the others and will barely work, thus straining the rest.

That is why we never use NTE parts. Not because they are crappy, but because they are not like the other parts they must work with.

[Jerry]

Thanks for your help Enzo. There's one xstr blown on one side. I'm going to replace all four as the owner gigs a lot and they play pretty loud. From reviews of the amp it sounds like this is a good one for him.

[Enzo]

Just make sure to run a signal into it and have it drive a dummy load at about half power for an extended period before you release it. A transistor on the other side MIGHT have been stressed, give it a chance to blow.

[acousticcontrolcorporation]

www.acousticcontrolcorporation.com

You guys definately need some troubleshooting help on Solid-State amplifier techniques!

Doug Forbes

[Robert M. Martinelli]

You guys definately need some troubleshooting help on Solid-State amplifier techniques!

Doug Forbes

Doug,
First of all, hi and welcome!
You will excuse me if I go off the "technical path" for a moment, but I think the true spirit of this forum to be something completely different: I find it a great "place" to share ( and possibly gain ) knowledge, a "place" to get and offer help, so I find your attitude to say the least inappropriate.

Maybe what you say it's true, but, again, you could have given some useful advice ( all the more so if you're so keen on SS amps troubleshooting ) instead of posting your rather "impolite" statement.

I'm into electronics since the age of 8 ( 45 now ) and I find a great sense of accomplishment when I manage to help someone or share my little knowledge. I consider it my tiny contribution to a better world.

I am sure you have a lot to give, too!

Now it's your turn!

Peace

Bob

[Enzo]

We are certainly open to additional voices on the solid state front. SInce this board is dedicated to tube amp tweakers, we are lucky to have as much SS as we do.

One thing I like to teach is that troubleshooting is troubleshooting, and it doesn;t really matter what the technology is.

[jrfrond]

You guys definately need some troubleshooting help on Solid-State amplifier techniques!

Doug Forbes

I am curious as to what prompted you to say this.

[acousticcontrolcorporation]

Solid-State Power Amp Test #1

Most all solid state amplifiers without extensive protection circuitry can operate without ANY power transistors in the output. Of course, you will not have any load (speaker or otherwise) attached when powered up for the test. Attach your oscilloscope to the speaker jack and power it up. Look for any deviance (anomalies) from the injected input sine waveform. You can now look for clipping and test tone controls, effects loops, gain circuits, etc. before the output stage is even in the circuit. Also you can leave it powered up and look for spurious oscillations and heat before the output driver transistors are installed.

This works on many of the acoustic models (except 130's, 140's, and 150's due to the output driver transformer.)


Doug Forbes
DEF Audio Consulting

[randomair]

I am curious as to what prompted you to say this.

I second that.

[acousticcontrolcorporation]

Sorry ~~~ Accept my retraction and apology!

Cut and pasted from letter into post accidently. Only cut part of text and posted into wrong thread. Too many open threads at once. Im not used to forums or chat.

Sincerely,
Doug Forbes
DEF Audio Consulting

[Jerry]

Thanks for the tip Doug!