SS amp blues...

[dkevin]

I am taking a look at a SS amp for a friend and am more than a bit lost. It was described as "humming loudly with just a bit of guitar signal audible". Then it "buzzed" and blew out (fried) the test speaker. It has obviously been "looked at" before but shows no obvious signs of arcing or burning.
I read 53vdc on the speaker jack and 106vac on the same jack. Could it be that he has fried his rectifier in addition to having main caps that are toast?
Also, if there are recommendations for reading material on SS amp repair, please let me hear them. I don't plan to make this a habit but I do own several SS amps of my own and would like to understand what's going on under the hood and how to troubleshoot these beasties.
Thanks for your help!!!
dkevin

[Jazz P Bass]

SS amp

Can you tell us the brand & model of the amplifier.
53Vdc on the output is a good indication that the output section is compromised.
(ie: blown)

[dkevin]

amp id

The amp is a "Road" model 220 lead amp mfg by Road electronics Inc in Fort Scott, Kansas. It is a real beast of an amp!

[Jazz P Bass]

Road 220

Here is a nice link.
I would take it to a reputable tech.

Link:Pre-Rickenbacker Road 220 - TalkBass Forums

[J M Fahey]

I used to repair them in the late 70's.
They had the schematic glued to the inside of a sheet metal cover.
Can you scan and post it?
Just by heart, I remember they had a Fenderish tone stack, a beefy quasi-complementary bipolar output stage (all NPNs), huge transformers and filters, their trademark heat-sink-in-the-roof and a funny distortion circuit, coupled to a high pass filter (did it have a real inductor?) that made it even buzzier.
But the EV speakers and the high power (250W RMS) made it a beast onstage.

[dkevin]

No schematic/no luck

The link posted earlier to Rickenbacker amps was a great help. Looks like a distant relative of the Kustom amps. However, there is no schematic located anywhere in/on the amp.
This friend is gonna want to get some advice as to the repairability of the amp. I think he paid approx. $75 for the amp- is it likely to be worth sending it to a tech? Does anyone have a guesstimate for the value of a head like this?

[Euthymia]

Also, if there are recommendations for reading material on SS amp repair, please let me hear them. I don't plan to make this a habit but I do own several SS amps of my own and would like to understand what's going on under the hood and how to troubleshoot these beasties.

Here's the best book I know of for solid state troubleshooting, and it looks like there are a bunch of them available for under $5.

[ame=http://www.amazon.com/Electronic-Troubleshooting-Student-Text-Olesky/dp/0026763907/]Amazon.com: Electronic Troubleshooting: Student Text (9780026763905): Olesky: Books[/ame]

[J M Fahey]

Hi DKevin.
I guess the actual price paid is irrelevant, because if you happen to want another, you won't get it easily for $75.
The real comparison must be :
How much will a (used) beefy, well-made 250W bass amp cost me today?
How much will it cost me to repair it?
*or* ou can buy new for $299 a "famous trademark" chinese (or vietnamese), poorly made 200/300 W bass amplifier, with lots of problems built-in.
Really don't know the repair costs, but you might try to measure the output and driver transistors for shorts, (you have at least one, guaranteed), replace them, plus some fried power resistors, and probably be rewarded with a reborn amp, risking a relatively small amount .
*I*'d do it, you can be sure, at least to practice.
And if it does not work, don't junk it, maybe in a near future you can tackle it again , with somewhat more knowledge or confidence, and succeed.
Well, maybe that's why you can't even walk in my home, chock full of dead mummies awaiting resurrection.

[dkevin]

To all mummy collectors....(that's you, JM)

So, someone else has the disease besides me! I have a few mongrels awaiting my illumination and healing. I scratch my head and try, try, try and then they go out to the garage to take a time out. Sometimes I actually run across the information I need in order to fix them. Otherwise,... I have a good-sized garage....
As regards the Road amp, I will advise my friend to hang on to it in hopes that someone who possesses more knowledge than I will offer to replace some of the mentioned parts. I will, in the meantime, pursue an understanding of solid state amps and how to trouble-shoot them. Who knows, I may even figure out what's wrong with the tremelo section of my Musicman 212 HD-130. I have paid two (supposedly) competent techs to fix it so far and it remains inoperative.