Flying components...

[mnexsen]

I picked up a point-to-point tube amp as a project. The amp (supposedly) has iron from a Hammond organ, 5Y3 rectifier, 2 x 6V6, 3 X 12AX7''s on a homemade chassis. It works, doesn't have a lot of clean headroom and sounds pretty "brittle" but should at least be a backbone for playing around. My biggest concern is that all the components are just soldered together and flown above the chassis. This doesn't seem very robust to me--should I put a tag board in? I don't see any kind of bias circuit (I haven't looked really hard yet.)
The amp is laid out on a sort of 5E3 design where the chassis sits vertically in the cabinet with the tubes on the rear. I'm wondering if I can just get a schematic for something with a similar tube complement and rebuild this to suit my needs. Any thoughts? One more question: The OT is wired for 8 ohms now. There is another pair of leads cut off; I'm wondering if these might be 4 ohm leads. How do I test this?

[R.G.]

My biggest concern is that all the components are just soldered together and flown above the chassis. This doesn't seem very robust to me--should I put a tag board in?

The present setup is a disaster waiting to happen unless each end of each component is soldered to a socket pin or terminal strip pin. Flying components are almost certain to someday either crack from repetitive mechanical stress or flex into each other or the chassis.

The OT is wired for 8 ohms now. There is another pair of leads cut off; I'm wondering if these might be 4 ohm leads. How do I test this?

You put a small test voltage into one of the speaker outs. 6.3Vac from a filament transformer should do. You then accurately measure both the voltage going into the tranny and the voltage across each winding. Oh, yeah - for doing this, all windings must be open circuit, no connections.

Then you can compute impedance ratios from the measurements. Impedance ratios are the square of the voltage ratios. If you know the 8 ohm winding, and you find that the voltage on the two mystery leads are 1.414 times the voltage on the 8 ohm winding, then you have found a 16 ohm winding. If you find that the unknown voltage is 0.7071 times the 8 volt winding, then you have found a 4 ohm winding.

Be sure to measure to those cut off leads before you get into this. If they are all continuous with the 8 ohm leads, you probably have a tapped output, which may have 16, 8, 4 and return leads. Pick the return lead to put one of your voltmeter leads on, measure to all three of the leads if this is the case. Same voltage ratio issues apply.

[mnexsen]

Thanks for the reply. The construction didn't look great to me, but I wanted something to tinker with anyway. So, given that I'm going to basically completely rebuild this amp, do you have any suggestions for a good model to build? I have a Silverface Pro Reverb, but was looking for something smaller and lighter to carry to gigs. The tube complement in this one suits me pretty well. I'd like to find a schematic for a Fender amp with the same tubes and just rebuild the guts of the amp, leaving the chassis and tube layout where it is.
I'm not experienced, but I have built a Chanp and replaced some caps. I'm lost when it comes to knowing what components to select: carbon film vs. carbon comp; which caps are good and which ones are crap. Is there a source to learn this stuff? I'm past the half century mark and might not have time to take the experience route...