First Timer needs help

[planet10]

Originally posted by mgalvez Can I make this amp sound good with speakers such as these?

... dayton3....

Not a good idea... ignoring whether or not the OPTs are designed for 4 or 8 ohm speakers (or if they have taps for both), the efficeincy on these is too low (~86 dB) and the XO (and the resultant bumpy impedance curve) are not going to be to the liking of 4W SE amp.

This amp can be made quite musical, and even just made to work can be surprisingly plesant. To get the best out of it, you'll just want to use it as an iron donor and rebuild from the gound up.

dave

[planet10]

What Eli has been saying is all good stuff... he did miss one very good option thou, and that is something based on the RH84.

http://www.tubeaudio.8m.com/RH84/rh84.html

The techique od adding the feedback from plate-to-plate comes pretty close to ging the sonics of running the outputs in triode and getting the power of the pentodes (which when you are talking amps this small is not insignificant)

The amp also tends towards current drive, so Eli's idea of an OB with a full-range driver is a good one. There are lots of decent vintage 6-8" drivers for almost nothing (many still hidden inside thrift store boxes). Between the natural bass limits on these drivers, how low you can get on a reasonable size OB, and the current drive, you probably won't notice any limitations in the bass from the size of the OPTs.

dave

[TubeHead Johnny]

I disagree with just about everybody on this thread. I seriously doubt that this amp is worth restoring. IMHO, replacing all the passives or rebuilding the unit on a new chassis (or a pie tin) is not going to improve the fact that this was a very cheap design and aways will be. Your not going to be very happy when you fire this baby up, only to find out it sounds like two paper cups with a string in the middle. It's just a waste of time. I would salvage the PT however.

What I would do first is maybe build an amp from a kit. AES (Antique Electronics Supply) URL=http://www.tubesandmore.com/
They have a couple of tube kits at a very reasonable price and I've heard that they sound really good. You start with all new parts and it will take most of the guess work out if something doesn't sound quite right. Plus, I'm sure you will have someone to call (or email) if you can't get it working right away. Someone who knows all about that specific amp. Are you good with soldering? I bet you can get this puppy running in a couple evenings. Also, it probably has a section in the manual about basic tube theory and electronics.

After that, I would try restoring something worth restoring. eBay's vintage gear is fetching ridiculous prices and getting more ridiculous everyday, but you can still find some good deals. Try looking for a 6BQ5/EL84 push-pull amp that pumps out around 10-20 watts per side. Not too long ago, I picked up a Dyna SCA-35, replaced the tubes, caps, and most of the resistors, and it sounds awesome!

Good Luck!

~~~John~~~

[mgalvez]

I really have been looking hard at El Cheapo. I spent a lot more on my amp than it was worth, so I am kinda stuck. I want to at least learn from it, but I also want something that sounds good. A kit seems easier, but I like challenges. My soldering skills are actually pretty good, I've installed quite a few mod chips into game consoles and have been into RC cars + planes when I was growing up. I used to make all my own battery packs with matched cells. I have gotten through a few chapters of a beginning electronics book, but there is a lot more to learn.

[SHiFTY]

Your not going to be very happy when you fire this baby up, only to find out it sounds like two paper cups with a string in the middle. It's just a waste of time.

I disagree- my 6BM8 amp was quite good sounding, even with cheapo output transformers. It was a good first project! With a bit of negative feedback the distortion is low, and it was definitely worth doing.

mgalvez- strongly recommend a rebuild to something like the schematic in my post above, if nothing else you will get some experience in tube circuits, plus a neat looking functional amp, with the total cost limited to the new components and some pieces of wood or metal as a cabinet...

If nothing else it can power your computer speakers!