Mono Tube Amps Questions

[SharkyRivethead]

So, I just bought a pair of diy, fix'em up tube amps. Model Bell Sound 2122-C.
They need some major cleaning. They also came without the transformers or tubes. Here are some questions....

I wanted to lay out the components and mount then on a pc board. I don't know, I wanted to clean things up and make it look nice. Is this practical? Should I leave everything hard wired/connected?

Second, when it comes to the components, should I look for original parts or replace everything with their modern equivalent? Does old versus new make a difference in sound qualities?

Thanks Sharky.

[A9X]

There's no advantage to a PCB in this application, leave it point to point. Clean it up, remake all the solder connections and replace the PS caps with fresh ones and see how they work.

A lot of newer passives are better performers than older parts, and some like carbon composition resistors can be very noisy compared to a modern MF or WW.

You'll need to find a schematic and work out what iron to use, but none of the tubes are hard to get and Hammond will most likely have something suitable for the PS and output iron.

As you have a lot of parts to get, it might be better to consider selling these on as is and building something from scratch. You could probably build a great amp like the Red Light District for the same money s a resto.

[blair]

Got any idea what you want out of them? Pics?

There are lots of options, but for the most part there is no need to go to boards. Tube are easy to work with.

[SharkyRivethead]

I will post a picture in a little bit. They are old and need a lot of work. That's the exciting part of it! These amps are from around the late 40's early 50's. I'm not in this for money, it's not my intention to re sell them. But to learn what makes the amps do what they do. I love taking things apart and reverse engineering them.

Now...as far as what I want them to do? Egads! Well, I am in the process of building a pair of dedicated 2 channel (L&R) speakers. I posted stuff about them some time back. The Giza project. It was my dream to have something that I built powered with mono block tube amps. I know, it's silly. I can't explain this need.

They will primarily be used for jazz, blues and classical. Though I have not picked the drivers for the Giza's, should I take that into consideration when reconstructing the tube amps?

[blair]

Dude,

justification is not needed

I just wondered about power needs, etc. If you want to drive 85db speakers with 10 watts, you might not get what you want or need. I had a pair of 160w monos driving my two channel setup for a few years before little hands came along.

Do your amps use big bottle tubes or 9 pin tubes. PP, you will probably not get much more than 14-17w out of 9 pin tubes. If you have to replace all the iron anyway and there are 8 pin sockets, you can get some decent juice out of them.

[SharkyRivethead]

Thanks Blair, most forums treat "newbies to that forum", like they have no clue.

The blocks tubes (power, rectifier, pre, 1st af, 2nd af phase inverter) ...just so that I'm clear (scratch statement above. lol) The sockets have 8 pins surrounding 1 larger pin. So, does that make them 8 pin or 9?

The photofact sheet has the amp @
Power supply 110-120 v AC
Rating .67 amp @ 117 v AC 50-60 cycles
Output Impedances 3.4 - 4ohms, 6-8ohms and 15-18ohms
80 watts

[blair]

That makes them octals or eight pin sockets which is good for someone who is getting started. More room to work with around the pins.

Are there any transformers at all on the chassis? If not then the photofact might as well be used as s solder drip pan

Edcor makes the best priced and highest quality trannys in the US that I know of. Phyllis and Brian are both excellent to work with. How many watts do you need? If the chassis are not large, and you just need 10-15w I would personally build a simple Single Ended amp using a KT88 or 6550 with a super beefy PS with lots of filtering. Feel free to shoot me an email. I think it is accurate on the forum.

Most importantly, be careful. Screwing up in a live tube amp can be lethal. I have been very fortunate on my days.

[A9X]

The photofact sheet has the amp @
Power supply 110-120 v AC
Rating .67 amp @ 117 v AC 50-60 cycles
Output Impedances 3.4 - 4ohms, 6-8ohms and 15-18ohms
80 watts

Note that the 80W is the power drawn from the mains, not what they put out to speakers. The originals used a pair of 6V6, class AB PP which means they are about 14W/channel.

I would definitely not build a SET with them. Either restore them or build something else.

[SharkyRivethead]

See, this is why I'm posting this stuff. I'm new to the tube amp thing and will have many questions and seek as much input as possible.

Really, all I wanted to do is restore them. So your right in suggesting that A9X. They are not the prettiest or the most powerful. But a good way of getting my feet wet. I know I have a lot to learn.

Blair, you made a comment that may prove problematic. These units don't have any transformers. It looks as though they had been stripped of most everything. Except the caps, resisters, plugs and dials. Unless I found the same transformers, it would be a waste?

[blair]

That was kind of the point. If the trannys are gone, then rebuiling them is not an option. Plus, were they hifi amps to begin with? I'm not disagreeing with the other posters, but it makes no sense to rebuild when there are lots of options.

Do what you want, but you really bought a couple of pieces of punched sheet metal. You might even have to replace the sockets. I'm not trying to be discouraging, but it is not a cheap to get into tubes and there are lots of beginner options. As far as the sugestion not to go SET, I'm not sure why you would not observe the option. Plus, it would not be a SET. KT88 and 6550 are both pentodes

[Æ]

Go ahead and rebuild them if you can. A worthy project, that if successful you could be very proud of and I'm sure the "sound" will be quite nice. Just be very careful if you don't know what you are doing, tube amps have some very high voltages.

See, this is why I'm posting this stuff. I'm new to the tube amp thing and will have many questions and seek as much input as possible.

Really, all I wanted to do is restore them. So your right in suggesting that A9X. They are not the prettiest or the most powerful. But a good way of getting my feet wet. I know I have a lot to learn.

Blair, you made a comment that may prove problematic. These units don't have any transformers. It looks as though they had been stripped of most everything. Except the caps, resisters, plugs and dials. Unless I found the same transformers, it would be a waste?

[A9X]

Really, all I wanted to do is restore them. So your right in suggesting that A9X. They are not the prettiest or the most powerful. But a good way of getting my feet wet. I know I have a lot to learn.

Blair, you made a comment that may prove problematic. These units don't have any transformers. It looks as though they had been stripped of most everything. Except the caps, resisters, plugs and dials. Unless I found the same transformers, it would be a waste?

As was mentioned, you have a cheap old piece of stamped steel for a chassis, and some sockets and passives of questionable quality. having done lots of restorations (still have a Fisher 800B on the bench being 'resto-modded'), unless there is a desire to use those particular units for sentimental reasons (Grampa's amps for example) then a better bet for a beginner is to start with a kit or a scratch build, especially as you are starting with very little anyway. Having googled for pics and schematics of your amps, without iron or tubes, there is very little I would bother using of what's left myself given the choice.

As far as the sugestion not to go SET, I'm not sure why you would not observe the option.

Why would you? Inherently output power restricted and hobbled in performance by an OPT that has to be gapped to allow DC which greatly reduces primary inductance and effectively unloads the tube as frequency decreases.

If you must worship at the altar of class A tube, class A PP is a much better solution.

Plus, it would not be a SET. KT88 and 6550 are both pentodes

When you wire a pentode as a triode, it is then a triode.

[blair]

OK.

I suggested the SE amp because it is his first build and you can do it with less than a handful of parts. Not because of any alter.

Yes, they function as triodes IF you strap them that way, but I did not mention that.

I suggest you listen to A9X. He obviously knows much more about these builds than I do. I'm still available on PM if you are interested.

[A9X]

I suggested the SE amp because it is his first build and you can do it with less than a handful of parts.

The altar comment was tongue in cheek, but a class A PP or even an AB1 PP doesn't require much more work to build.

My fave small amp build is SY's Red Light District as it's an exceptional little amp and can be built with aftermarket Dynaco iron. It's a bit more complex than a typical beginner build, but well worth it if you're a bit brave and looking to have a good amp at the end, and not just a learning process. This is only one suggestion out of many out there.

I'd also suggest very, very strongly that any new tube amp builder invest in Morgan Jones' Valve Amplifiers and Building Valve Amplifiers. Exceptional books and very clearly written in as simple a language as possible.

I'd also strongly suggest you take some time to read this high voltage safety thread on diyaudio. And then follow it.