DCAudioDIY.com

from a friend, he deals in vintage amps as well as other stuff, makes a good living at it...

I remember my first amp well, and I still have the schematic. I copied the circuit from a 1950 vintage television audio output section--something like a 6AV6 to 6V6 single ended. Cannibalized old TVs for parts and the cost was $ 0, even building on old chassis sections. I later expanded my knowledge by copying preamp and tone control sections from the RCA tube manual. Again cost was $ 0 because I had plenty of left-over parts from all the TVs. This amp sounded wonderful to me at the time. Unfortunately you can no longer go into a TV repair shop and ask them if they have any abandoned TVs they would like to get rid of, at least not of the vintage I got at the time.

David

Of what years could I expect to find a tube amp inside? Are there certain brands that were known to build quality units? There is a shop in Baltimore that has an old Magnavox console. It still has the tuner and turntable inside.

I have seen quite a few small tube amps listed as hybrid amps, but most say headphone amps, so I am assuming they wouldn't have the necessary power. I ended up finding a few more, but some of these are already built. Not saying that is a bad thing, but I liked the idea of putting it together too.

http://www.amazon.com/Qinpu-Q-2-Hybrid- ... B001TGDB9Q

http://www.amazon.com/Stereo-Integrated ... be+amp+kit

http://www.parts-express.com/yuan-jing- ... --320-6552

http://www.amazon.com/Nobsound-MS-10D-a ... be+amp+kit

The last one is really classy looking, though there is something really cool about the plexi or lexan ones that you can literally see all the internal components.

Qinpu seems to be a more affordable amp company, some of their products have quite a few great reviews. Are tube amps one of those things that you can get a cheaper amp, and spend some money down the road for better tubes and greatly improve the sound?

No, not really. A crappy sounding tubeamp is not going to get miraculously better by rolling in NOS tubes.

All that kits you listed probably have fairly (extremlely?) cheap PT and OT. The power supplies look marginal/minimal and they probably will be fairly noisey and not sound all that good. Those look like the 12ax7/EL84 console amp I built except my iron was made in the USA. The real advantage to building one yourself will be to learn the basics. Stuffing a premade circuit board will teach you how to solder but that is it. Paying $200 for a new retail product tube amp is NOT goingto get you much other than cheap circuit boards, cheap chinese PT and OT.

I've got some little SE output transformers I could send you, Edcors I think. I'm not going to use them. They're not terrible high-end but they have decent mid-range and make music. They're 2.5K primary, 10 watts or so, good for 2A3, 300B or triode-wired KT88. I also have some Chinese 2A3s you can have. I might also have a surplus power tranny in my stash. Once you get the trannies together, the rest of the expense is minimal.

I really appreciate you offering to help me out. I'm really excited about the prospect of building my own amp. The tough part I am realizing is that its not even that cheap to build a turd of a tube amp, so to build one of quality is pretty pricey. Don't want to build a piece of junk I won't ever listen to, that would defeat the purpose, so any parts you don't mind parting with that could help me complete one would be a huge help.

I found a website that has full schematics of a lot of different kinds of amps. Its been interested to see the diagrams and amps side by side. Even read some of Nelson Pass's pages on amps. Guy is insanely gifted in the amplifier arena. Feel a bit stupid reading them though, he uses a great deal of technical jargon I am not familiar with.

An old stereo amp/revceiver can provide the output iron you need, cheaper than new. HH Scott and Fisher pieces had EXCELLENT iron. Edcor can provide very nice iron brand new, SE or PP and power transformers. You can save some by using Antec toroidal transformers, but here we are compromising again.

Build on an experimenter's platform (a wood shelf plank, etc.); play around and see what sounds good to you. Learn. Don't worry about looks or practicality at this point. Build so that you can change configurations or iron at will.

We can help (kind of like the Home Depot, but without the orange aprons)

Stuart

I had some extra circuit boards for a little 10-watt ZOTL (output transformerless) amp that I decided to go ahead and build up without an immediate need for them. I would want to get $850 for one of them, and they would need to be put into a chassis and additionally supplied with 300-350 vdc (obtainable from a simple voltage doubler off the line). Isolation is not needed as they have their own isolated power supply-regulator built in. They are low in gain, and an input gain stage such as a 12AU7 would be recommended to bring the sensitivity up. Voltages would be available on the board to run such an input stage without having to build an extra power supply. Currently they are phase inverting and have a sensitivity of 5 VRMS in for full output. They have a 12AX7 driving a push-pull pair of 16GK6 tubes (similar in characteristics to the EL84). They are dc-coupled, with a bandwidth nearing 100kHz. They also have dc speaker protection and autobias.

I toss this out there as sometimes someone asks me about a kit for one of these ZOTLs and I have never offered one because of the complexity. This would be a "partial" kit that would require the DIY person to do some of the work and perhaps customize something that could be very good in the end.

This project should not be considered by anyone not familiar with safety procedures required with the voltages present in tube amps. These amps have dc voltages as high as 650 V and peak voltages reaching up to 1100 V or so. Also, proper knowledge for constructing the line input rectifier-doubler circuit and fuse, on-off switch, etc. is needed. I provide schematics of the board, and would provide recommended circuits for the line doubler and 12AU7 gain boost if needed.

David

I am selling an Eico SCA-35 tube amp presently on ebay. It would need to be cleaned and rebuilt with tubes and caps, I believe a number of members have done various mods to this amp, and I would recommend Dave Gillespie's EFB for this model (there is a lot of info on EFB on audiokarma and its use on numerous vintage amps) I could drop it from ebay and let you have it for $210, expect to put around $150 for tubes, parts, etc. into it. Close to your price point, it is considered quite a good-sounding amp. I am sure some members can add their observations to sound quality, mods, etc., the output trannys are quite good.

David, that is a very generous offer, and I really appreciate it. I wish I had the necessary funds to purchase it as it sounds like quite a setup. As I am still learning about tube amps, I find myself googling many things you put in the description. Truly had no idea all that went into making a tube amp nor the endless options and methods employed to achieve the same result of great sound! I looked at your website, and while I am sure you hear it all the time, it still needs to be said, you do some amazing work.






Randy,

This too is a generous offer. I tried to look up Eico SCA-35 tube amp, but nothing comes up. Is it a Dynaco SCA-35 ? as that comes up quite a bit.

To be honest, I am not sure I am quite ready to get something. The reason I say this is there are so many different kinds of tube amps. (My apologies for such a stupid thing to say) I have never seen the inside of one, nor had one, so I am truly learning every time each of you suggest something. David's mention of the ZOTL was the first I had heard of an ouput transformerless amp. I just didn't realize all the different styles, terms, models, etc. It's honestly a bit overwhelming. Its hard for someone with little to no tube amp knowledge to understand the differences between a push-pull, single ended triode, pentode, and tetrode, Class A , AB, C apparently (Had no idea there was a class c amp. With speakers I can usually tell quality by looking. Looking at the construction methods, the quality of veneers and types of veneers, and even the drivers have indications of quality. Sure some are deceiving, but the 100K Tidal speakers I saw at CAF, looked like they would cost 100K. Not that they should, but they looked as though they would. Same with speaker cables that are $2500 per linear foot. Looking at them, you know its going to be expensive.

Tube amps on the other hand seem a bit deceiving. They look very simple, small chassis with tubes and transformers on top, usually not much flash or anything like that. Some very simple looking amps cost more than 10K though. It is, for me at this point, very hard to see differences in quality. Given the numbers of websites I have visited researching this project idea of mine, I have seen 100 dollar hybrid amps (still don't know what that means exactly) all the way to 10,000 dollar amps. Interestingly the chassis' are usually similar, brushed aluminum or wood, the tubes look similar as well. The only thing to the newcomers eye is the size and number of transformers on the top.

So because of this I feel like its a bit too soon to make a decision on which way to go. While I do trust all of your judgement on these matters, it seems shortsighted of me to try to rush to the finish line. I would hate to buy an amp or build one, and not have a good understanding of what does what, why each component is needed, and where value comes into play with each of those components. Thanks to all your input and advice, I feel like I am on the right path though, and for that I am very grateful

Jeff