Testing a cutting amp using a speaker

[smithadamm]

I just rebuilt one of my cutting amps. I want to do a general test on it before hooking it up to my cutting head. Nothing fancy, just checking to see if it passes signal at the impedance the head is going to be, maybe a real crude frequency response test. Can anyone think of any reason I shouldn't just hook it to a 16ohm (my head impedance is around 14ohms) speaker that can handle the watts? The amp is solid state.

[tragwag]

I brought my Presto 92 series amp to a tech once, he played a radio through it the whole time to test.
it sounded beautiful! almost a shame I have to feed it only RIAA encoded signals...

so in short, yes do that, no reason it would harm it at all.
What amp are you speaking of?

[smithadamm]

What amp are you speaking of?

Thanks! I figured so, but I wanted to check in with the brain trust here.

It's a Ransteele RPA-250. A big 70's solid state 240W RMS mono amp. Sounded really great right up until it stopped working.

I used the opportunity to swap out all of the carbon comp resistors with metal film, replace all of the power resistors, re-cap it, and change and re-heat sink the power transistors. On the bench everything is testing good, but I want to check it out without the possibility of blowing up my head.

[opcode66]

There is no difference between a speaker and a cutterhead electrically. They are both coils. You would want to pick a speaker with a similar DC resistance. If you don't, you could be overtaxing your amplifier. And, then you certainly could have some issues created in the amp! So, as along as the speaker is a similar resistance, this is fine. If not, you risk damage to components in your amp.

[tubefan]

Hmm, Ransteele? Do you have any pics?

I know of someone with two hand-wired Ransteele audio racks, no schematics or documentation. Curious to see if it is similar. It was an odd company, I had a Ransteele Neumann lathe, it was an AM32b painted white (awful) with a Sontec Compudisk and a Technics SP02.

[smithadamm]

I've got no documentation on mine either. I know someone else that has a couple of the 250W amps and he doesn't have any paperwork. I found someone on google that had one that was a re-branded/modified Dynaco hi-fi amp.

They are easy enough to work on, the design is a really straightforward class A solid state design, but it can be slow going without schematics.

For all my griping about not having paperwork, I do think it is a really great sounding amp.

This is the left cutter. As you can see by the date scrawled on it, something happened to it on August 19th, 1984. I'm assuming it was made then. My pre-amp is Ransteele too, but it is at the studio. I'll post pics of it here at some point.

[pdmillar]

Those driver transistors with the weird integral heat sink look just like the ones in my 70s Acoustic bass amp... are they made by RCA?
Mine failed and made full-voltage-excursion crackling noises happen at the output of the amp.
Some of them look like they were replaced with a different type with less heat sink mass, which makes me kind of nervous. Try and locate some NOS replacements if you can.

[smithadamm]

Those driver transistors with the weird integral heat sink look just like the ones in my 70s Acoustic bass amp... are they made by RCA?
Mine failed and made full-voltage-excursion crackling noises happen at the output of the amp.
Some of them look like they were replaced with a different type with less heat sink mass, which makes me kind of nervous. Try and locate some NOS replacements if you can.

Yep RCA. They are still working at the moment, but I was thinking I should have some spares on hand. Thanks Paul.