Tube integrated question

SDA1C

I don't fully understand the concept of bias and all the adjustments and such of tubes and know it would be expensive for me to attack that learning curve. I am looking for a 2-8 watt integrated but don't want to have to set the bias and such. Are there amps that stay set or do not require this to realize peak performance?

Also, my intention is to set up my 5jr+ to a flea in the bedroom. I would like to build it from a DIY but though I have the mechanical abilities and am handy with the iron I do not know the electronics well enough to have the confidence beyond the actual assembly. I could part with 5 to 7 hun for this project but have no idea if that is enough or not. Any help or suggestions would be greatly appreciated.

michaeljhsda2

Some amps like Yaqin have the bias points on the outside of the case making adjustments super easy and safe. I would avoid buying an amp where you have to take the cover off to make the adjustments as there's about 400 volts inside that can kill you.

zingo

There are many tube amps that have auto-bias, so you are in luck. The difference is you usually need to have matched output tubes for auto bias, where as it is not required for manual bias.

There are many tube amp projects you could use to get started, but I don't think any of them would meet your expectations for sound quality. Most people have to learn on a cheap/easy one, and then graduate slowly to more complex projects. Working on tubes can kill you as some B+ power supplies can be in excess of 600V DC with large filter caps. Plus, if you screw-up something on an amp you have a lot of money into, are you going to be able to diagnose and fix it?

SDA1C

I know I won't be able to diagnose any problems. That's the problem lol. I can fix the hardware easy piesy but knowing what to fix is a different story all together. Know any thing about the 6 moons? amps.

SDA1C

michaeljhsda2 wrote: »

Some amps like Yaqin have the bias points on the outside of the case making adjustments super easy and safe. I would avoid buying an amp where you have to take the cover off to make the adjustments as there's about 400 volts inside that can kill you.

Id rather not adjust anything. Autobias seems like a good deal. Are they as accurate and all that. Sound as good as bias adjust on the fly? Do you adjust under load? I wouldn't even know what I am looking at if I did out a meter on it.

zingo

Low Power Tube Integrated Amps:
http://shop.grantfidelity.com/Shuguang-I-12-Integrated-Mini-Tube-Amp-w-headphone.html
http://www.ebay.com/itm/Small-Mini-Tube-AMP-Audio-Amplifier-APPJ-EL84-12AX7B-Original-Miniwatt-N3-1set-/251007931870?pt=Vintage_Electronics_R2&hash=item3a713d15de
http://www.jolida.com/product/glassfx/fx10

SDA1C

Do you know if the Jolida FX10 is common ground? I know the 5j don't need it but I will try it on my 1c's for sure. The ebay one looks a bit lower quality than I would like and though I have heard descent things about Shuguang I prefer the US company.

zingo

DIY amp kits:
http://www.bottlehead.com/store.php/products/single-ended-experimenters-kit
http://www.tubedepot.com/diy-k-8ls.html

zingo

The APPJ EL84 is apparently the same internals as the Miniwatt, so I'd have confidence buying one.

SDA1C

Are you familiar with the S.E.T. Baby? Any thoughts. I have seen the Bottlehead offerings as well as the ones from Decware and the like. I am not sure at this point a kit is what I need to do. I should probably look at the assembled ones and do some reading before trying to kill myself LOL.

SDA1C

Is the bias a set it and forget it thing or how often does it need adjusted? I am getting to a point in my journey where the music is what I want not the tinkering. I do not think I would be satisfied with something I need to adjust every time I want to listen.

Are common ground tube amps the norm or do they tend to remain non common?

SDA1C

If this tutorial is anywhere close to the procedure I am in no way looking to bias my own amps.

http://www.guitargeek.com/chat/amplifiers-9/picture-tutorial-biasing-tube-amp-81368/

organ

I know it's not what you wanna hear, but look at it this way. You want to DIY this amp. This requires 1000x the amount of work vs biasing. Biasing only takes 30 sec.

Biasing is simple as pie when access to it is easy. All you need is a multimeter and you adjust the pot. Both are usually external. You keep an eye on the bias for the first day or so on new tubes. After it's holding stable, check again after about 25-50hrs burn in, adjust if needed and you're set. You'll only have to check every few months after that. And I'm talking about adjusting very small drifts in the initial installation.

SDA1C

That seems fairly simple and straight forward. It seems to me that the knobs that I thought were for bias are for something else? does the bias change when you change volume? What other than burn in has the biggest effect on the bias? It really is sounding like a set it and forget it deal. I can do that if its not a set once a week thing. If it is off what happens? Sounds like crap? Catches my house on fire?

organ

If you see knobs on a tube amp, they're usually for the bias. Of course, check the instruction book if they're not labeled on the amp.
You bias when the amp is idle. And that's it. The bias voltage/current will jump up and down while music is playing, that's why you do it with no music playing. No, you don't need to bias when you change volume.
After burn in, the bias will usually drop very slowly as the tube age. I'm talking slooooooow here.
I have a few amps that require manual bias and after burn in, I didn't have to adjust the bias for at least 3 months on one set of tubes. And at that time, it really didn't need it. The drop was so slight that I probably could have left it for 5 months without adjustment. But still better to check every month or two just to be safe. Sometimes tubes go bad.
I find that the amount of adjusting needed usually depends on the tube. Some brands take a little longer or less time than others.

If the bias is way off, the tubes will break. I have heard of tube amps catching on fire and the fuse still hasn't blown. Just like any electronics, if something goes wrong, there is a chance for spark or fire.

When I install fresh tubes, what I do is, before turning on the amp is set the bias adjustment at minimum. I turn on the amp and let it idle for 30 mins and then, bring up the bias to the proper values.

I'm telling you, by the time you do your first bias adjustment, you'll laugh at yourself and wonder why you spent too much time thinking about something so simple. I know because it happened to me on my first amp lol.

michaeljhsda2

organ wrote: »

I'm telling you, by the time you do your first bias adjustment, you'll laugh at yourself and wonder why you spent too much time thinking about something so simple. I know because it happened to me on my first amp lol.

So true

SDA1C

I have to wonder...if it is that easy, and I do not doubt you, what is the reason to go to an autobias platform? Is the sound different between the two? Any advantages one way or another?

michaeljhsda2

I think the autobias tube amps cost more. There shouldn't be any sound difference between the 2 types that I can imagine. Buying a matched quad of tubes will cost more. I like knowing what the bias reading is at any given time and it's easy to measure with external access.

heiney9

michaeljhsda2 wrote: »

I think the autobias tube amps cost more. There shouldn't be any sound difference between the 2 types that I can imagine. Buying a matched quad of tubes will cost more. I like knowing what the bias reading is at any given time and it's easy to measure with external access.

Actually there is a difference because the two circuits are different. Generally fixed bias amps have more power relatively speaking, than cathode biased amps. Certain well liked tube circuits can't do both, so fixed bias are usually one or two types of circuits each having a different distortion characteristic compared to cathode biased amps.

There is a plethora of info on the 'net. Get your learn on.

michaeljhsda2

Aside from more power, which sounds better in your opinion H9?

SDA1C

Ah. so the auto bias need matched tubes or close because you don't have as much control over grid voltage? The two circuits the resistor bases vs. pot adjustable? I would think a swinging signal would be more musical.

organ

Just don't let auto/manual bias be a determining factor for you. There are great examples of both out there.
I have two self biasing and two manual bias amps. I like all four of them. I can have anyone demo all four in my rig and I can guarantee you, nobody is going to be able to pick out which one is self bias and which one is manual. My favorite amp is self bias. I also have one of my manual bias amp being converted to self biasing by my tech.
The actual circuit, parts quality, and very important, output transformers play a much bigger role in sound quality, IMO.

SDA1C

Lots of options here I can see. I have noticed what seems to be a very simple process to adjust bias on those that have accessible controls. I will be opting for one with that feature. I do not see it being a good idea to have to remove the covers on anything with that kind of voltage. I saw the quote" I'll gladly pay my tech 40 bucks to take the jolt" haha.

dudeinaroom

Or you could have your tech mod it for external bias test points. It's not that hard to do, would take around an hour to do.

SDA1C

That is another issue all together. I do not have a tech nor do I know of one, other than Decware, anywhere close to me. I do not know if he is taking new clients but last time I called he was very busy. Me not being the drop it off and wait for a call type of guy immediately excludes those that won't let me watch. Is the sound differences going to be based on the tube selection or the circuitry or both? I know both to some degree but what woll be most noticeable?

organ

Dude,
I thought about that. What happened is that I had the stock pots installed externally at first. I have 3 other pairs of 300B and the stock pots doesn't have enough range for 2 pairs. I know I can get pots with more range installed, but decided to just go ahead and do self bias because I really don't like messing around with 300B tubes where the cheapest pair are over $200. If I don't hear a difference, I'll keep it that way. If I'm able to detect a performance loss, I can always have the bigger pots installed.

SDA,
The output transformers make the biggest difference in tube amps. A good power supply is also very important. Tubes, imo, is personal. People have preferences because different tube types have their own unique sound character. For circuits, the simpler ones usually give the best results (SET). The parts count on some amps are so low. A lot of the good amps are point to point wiring and don't use any circuit boards.
So if one wanted to build a tube amp, first you would choose the tube type you want to use and find the best output transformers you can afford for that particular tube type. Then decide on the circuit design and power supply.
When you buy a tube amp, most of your money is going towards the output transformers.

SDA1C

Point to point seems like the way to go. I am definitely a firm believer in the less in the path the better.

SDA1C

Thanks Dskip. I am looking for the upper end of the flea category though. 15 watts MAX. Do the same limits apply to flea amps? Is it fair to say that lower wattage is lower cost or is the cost dictated by quality alone?

dudeinaroom

If I were you I'd go with a refurbished Scott 299, if you can find one. Great little amp. Modding them for four test points is pretty easy. All you need is four short lengths of wire, four test points, four resisters and a little guidance. IF you were to look for one you would want the one with the 6 pots on the chassis. There are 4 models of that amp, with some transition pieces in the mix. I really like the sound of the vintage sherwoods, but there layout leaves something to be desired because of heat buildup. Besides modding it for test points would would be more than what you would want to tackle.

Organ, I personally do not like the design of SET amps. Give me a good push/pull design and I am more than happy. From what I have seen and heard from others a good SET amp would cost more than a great push/pull.

SDA1C

when you say push pull is that in reference to the "swinging" signal. Also, I know this is a newb ? but ah well right lol. Are the tube amps in old organs the same thing? I know they would look different but do they function the same?

organ

Dude,
That's cool. SET is not for everyone. Your speaker selection is very limited with SET due to low power and very low to no damping factor. To get the most out of them you need very sensitive speakers (over 90db/w/m) and flat imp curve. So far I find Lowther and Fostex drivers to work best on them. Lowther and Fostex don't need any damping on the amp because their oversize magnets act as damping. I like both P/P and SE, but my preference is towards SET.

SDA,
Push pull refers to using 2 or more tubes per channel. You have one tube that push the speaker forward and another tube pulling the speaker back. The result is higher power output and damping compared to single ended. Single ended tube amps use a single tube to do both. Both push pull and single ended have their ups and downs. Push pull can power more variety of speakers while single ended sound best with certain types of speakers.
I don't have that much knowledge on old organ amps but the one I have tried is a single ended.