TV Horzontal Output Transistor for output stage..?

Horizontal outputs are basically fast switches and not very linear. They are designed to drive the flyback transformer for hi- voltage to the picture tube anode. Besides, 2N3055 isn't a great audio device either.

This xls file of some On Semi devices may help you...;)


  • some audio
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The gain is generally pretty horrible for horizontal output transistors as a consequence of the very high collector voltage ratiing. There's enough good stuff around at reasonable prices that you dont have to mess with the likes of horizontal output transistors or 3055s. If you look at the specs for a 3055, they are pretty much optimized for cheapness rather than performance.


Disabled Account
2005-05-25 2:25 am
I would say give it a shot. It may work. From the datasheet, it does seem to be a slow device (which can be desirable) and hfe drops pretty fast when hot.

But I guess as long as you don't push it, it should be fine as a driver or even output device in low-medium power applications.

I have been using switching devices in linear applications for a long time with good success (to me anyway). So i don't buy the stigma that some of us believe in.

BTW, Nelson also uses lots of switching devices in his amplifiers as well. Last I heard, they sound pretty good.

I guess there is to do with how one uses them, not what they are designed for.


Paid Member
2004-06-06 8:31 pm
Georgetown, On
You can use the ones with damper diodes, they are not going to conduct unless you put the transistor in backwards. The gain is dreadfully low with these.

I'll agree with wrenchone 100% here. Not only that, but these are normally more expensive than audio transistors. Unless they are fakes ('cause you got them cheap or for free).

Thank you...

Currently I'm using MJE13005. Because here in the local market, the power transistors which are easily available and cheap are those used in TVs and electronic ballasts. Choices for audio are 2N3055 and 2N3773. And yes of course... there is fakes.

I do not like to hear 3055 or 3773 anymore... the next choice is MJE13005 and BU508...! :rolleyes:

What I want to know was... wether the BU508 will sound better or worse (or fumes) than the others.

(Sorry... by mistake.. I've posted this message to an another thread)
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If you try too hard to polish a piece of ****, you just gum up your tools and get a lot of nasty stuff under your fingernails. I can't think of any real reason to try and use a horizontal output transistor for audio, except perhaps in Class A as a direct drive for an electrostatic speaker, (and that's a pretty big stretch of the imagination), or just maybe as an intellectual exercise if I had nothing else to do. I just pulled out my old Sanyo data book and took a look at the horizontal deflection transistors thay offer. Gain is listed a >8 at 1A collector current. - pretty shabby. I actually have some old 1500V Motorola horizontal deflection transistors that have a gain of one (no typo) at their rated drain current. I keep them around as curiosities, and they will probably still be sitting in my parts cabinet when I die, if I don't throw them out first.
I just took a look at the ST data sheet for the BU508. The gain falls very rapidly above 1A (below 10), so you would have to parallel a lot of these things and/ or drive them very hard in order to power an inefficient speaker. Other folks make the 508 (like MOSPEC), probably with worse actual specs. To be brutally frank, I would rather use a 3055 than these devices, even as much as I hate the 3055. If you are really that constrained as to the devices that are available, I would try to find some reasonable quality 3055s and build a modest class A amp. One way to do this may be to find some old linear power supplies and tear them apart.
Well, how about a post from someone who has successfully used HOTs in the output of an audio amplifier???

They worked very well for me. I made a simple quasi-complimentary output with them. As others have said, the gain is very low, therefore, good current is necessary in the driver stage.

Other than the bad gain, they sounded pretty good and worked quite well.

I'll try and get back with some numbers and measurements later, but the ears did say that this was a good project idea for somehow making use of those old TV transistors if you have any around (I have boxes of them from dead sets I have ripped apart.)


Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi Duo,
That's an honest appraisel. Your experience is perfectly valid. I doubt you would design a commercial amplifier this way. It did use some "free" parts and that's okay.

I tend to agree with wrenchone, given that audio transistors are not very hard to get at decent prices. There is something to be said about doing things the way they are normally done instead of fighting with the parts.

Well, I must confess that diy'ism highly involves using unusual or interesting parts to get the job done in my opinion. Remember when HK made history using TV tubes and transistors in their amplifiers??

Honestly, I feel that if you wish to use a part in a design, use any part you like. If you can make it work, then power to you. People who have done this sort of thing tend to be better at making things work anyhow. Also, they get good ideas!

I'm not saying that going with the norm is bad, but I'm trying to say that going against the norm is how evolution occurs!
Yes, I agree. For people starting out, it's best to use ways that other people are already used to. Thus they can come here, ask questions, and not confuse the answerers. haha

But certainly, I started out with well-known methods as well, and after I got tired of that is when I started to do things my own way to have fun.

It's how patents and miracles are born.