# I need TUBE amp help



## skittlesRgood (Oct 11, 2010)

check out what I found. no idea if it works or not but i was wondering if anyone knows anything about tube amps and could teach me about this one. if it does work im going to use it, not sell it. if it doesnt work... well if its a tube then it'll cost too much to fix. aren't tubes over $1000?














































pretend i know nothing about amps. i want to make sure i dont hurt this thing.


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## Silver Supra (Feb 15, 2008)

Tubes are NOT over $1000. What types do you need? Check ebay or audiogon.


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## skittlesRgood (Oct 11, 2010)

no idea what i need. have not turned it on. it may work perfectly well. i just want some one to teach me about using them so i dont mess anything up. this was my grandfathers.


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## Silver Supra (Feb 15, 2008)

The tubes should have numbers written on them so you can identify them. You will probably need to re-bias the circuit for the new tubes if you do replace them.

Turn it on and see what happens... they may be fine.


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## skittlesRgood (Oct 11, 2010)

do you know about tube amps? i would like more info on this thing. not how to work on it just yet. but how to use it. i mean simple stuff here. just being super cautious. tell me what everything does.


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## south east customz (Jan 17, 2011)

If you want to sell let me know.

It looks like an old dynaco, some were built in kits others factory. You should be able to find shop manual online for it.
I have a setup similar and had help from my old man refurbing it.
I wish I never sold it!!!


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## skittlesRgood (Oct 11, 2010)

nope, not a dynaco. its a knight kn 780 made my allied audio corp. i have not been able to find a manual for it. just a few specs and the numbers for the bulbs. i have no idea what the tiny knobs do on the back above the RCA inputs.


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## DanMan (Jul 18, 2008)

Thought this might help:
Knight Deluxe Stereo Amplifier KN 780 Radio Allied Radio Cor


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## stereo_luver (Oct 30, 2007)

DO NOT JUST PLUG IT IN TO SEE IF IT WORKS!

If the amp has been sitting for a long time you'll need to bring the power back up slowly to reform the caps. Plugging it in and giving it a try can result in a nice rebuild even when it may have been fine / semi-fine before you threw full voltage to the idle caps. A variac should be used to reform the caps and other internals slowly.

The Knight intergrated was a pretty good little amp. Depending on the tubes the output may vary on the power. The reverb unit is a little rare and could be sold to fund a rebuild. At 40wpc you'll find with some some efficient speakers this little bugger will really sing. Using EL34 tubes it will be very warm and detailed. The ECC83 tubes are the same as 12ax7's and that means you have tons of options on tube rolling for different tonal qualities. Look for Mullard, Telefunken, Sylvania and Westinghouse for the better 12ax7's.

The little 'knobs' above the RCA's are gain controls for the inputs to gain match the input loads on those circuits.

Cosmetics look decent and it should clean up nicely. If you should decide not to venture into the rebuilding or even want to chance the whole tube realm let me know. I'd snag this from you. Or trade some other home gear both vintage and newer.

Chuck


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## skittlesRgood (Oct 11, 2010)

DanMan said:


> Thought this might help:
> Knight Deluxe Stereo Amplifier KN 780 Radio Allied Radio Cor


thank you, but that is the one place i did already find with info on this amp.



stereo_luver said:


> DO NOT JUST PLUG IT IN TO SEE IF IT WORKS!
> 
> If the amp has been sitting for a long time you'll need to bring the power back up slowly to reform the caps. Plugging it in and giving it a try can result in a nice rebuild even when it may have been fine / semi-fine before you threw full voltage to the idle caps. A variac should be used to reform the caps and other internals slowly.
> 
> ...


ah ha, an expert has found me lol. how much do you think the reverb unit would go for?

the ground wire on the back of the amp, where should that go to?

someone on another forum said the tubes looked pretty used up. what do you think?

I have the problem of getting this home. i will have to ship it from arizona to california. think it'll be ok with enough packaging?

thank you very much for the info Chuck!


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## stereo_luver (Oct 30, 2007)

You can't just look at a tube to tell if its used up. I have tubes from the 50's that are just fine. Only way it would look used up is if the getter was smoked or the glass was all white inside showing that there was damage to the tube.

The ground is more than likely a point to ground a turntable and what that little wire is on it is a mystery to me. It should be fine to ship it if well packed. And as far as the reverb unit goes you'd have to do some homework to find a value.

Chuck


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## skittlesRgood (Oct 11, 2010)

the wire on the ground screw? or the wire in the revurb?

darn, I was hoping you would make an offer on the revurb lol.


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## skittlesRgood (Oct 11, 2010)

well... the gold face got a little bent in shipping because some padding came loose and wasnt covering the corner like it was supposed to. BUT the amp works as well as I would have expected a 48 year old amp to. I'm going to look into some new tubes for it anyways. might get a better sound out of the amp.

any tips on restoring this guy?


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## skittlesRgood (Oct 11, 2010)

so there are only two types of tubes in this amp? you know how many of each i need if i wanted to replace them all? im coming across "matched pairs". is that important?


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## skittlesRgood (Oct 11, 2010)

bump


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## stereo_luver (Oct 30, 2007)

Depending on how the bias circuit is designed will determine if you need to buy matched pairs of tubes or a matched quad. If the bias circuit has 2 pots to bias the tubes in a pair at a time then a matched pair will be fine. But if the bias circuit has only one pot then a quad will be in order. I'm not real familiar with this amp's topology so you'll need to find some more information on it.

Chuck


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## skittlesRgood (Oct 11, 2010)

i did see two pots next to the power tubes, they are next to each other too. just ordered a matched quad.

how to I measure the bias and what is it supposed to be set to?


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## stereo_luver (Oct 30, 2007)

I've put in a request for some info on how to bias this amp on another forum. Lets see if we get some answers. I suppose these may indeed be the bias pots on this amp pictured below.

Chuck


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## skittlesRgood (Oct 11, 2010)

Oh, thanks a lot. ya those are the pots that I saw. I guess I'll wait and see if you dig up some info for me. thanks again for going the extra mile for me here.


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## stereo_luver (Oct 30, 2007)

From Dave over on audiokarma.org:

Chuck -- Without a schematic or photos, it would be hard to give any specific advice, but in general, EL34s were typically biased to draw 50-60 ma of total current draw per tube back in the day, based on a typical B+ of 460-465 vdc. Beyond this, you're going to have to determined where this current was measured (typically in the cathode circuit), what value of shunt resistance is used at the measuring point (if no panel meter is provided), determine whether it represents one given tube or both tubes, and then do a little Ohms law to determine what voltage reading will produce the target current draw, as the situation dictates. Beyond this, a schematic will be needed. Good luck!

Dave 

You'll need to find an owner's manual (close to impossible) or take it to a tech for the answers. Sorry I couldn't help.

Chuck


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## skittlesRgood (Oct 11, 2010)

ok. well i have a friend I am going to visit this weekend who knows a good tube amp guy. maybe I'll see if I can meet up with him and get some info.

your helping me a lot Chuck.


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## skittlesRgood (Oct 11, 2010)

hmmm. just got new preamp tubes today and now I dont have any sound... just a low humming from the speakers and a louder humming from the amp. it worked before these tubes went in... any idea whats up with that?


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## skittlesRgood (Oct 11, 2010)

what a useful comment...

thetubestore already got back to me and said it sounded like two tubes are bad. ill have to test it this weekend.


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## lucius (Oct 2, 2009)

yea you should check out ebay and craigslist


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## skittlesRgood (Oct 11, 2010)

lucius said:


> yea you should check out ebay and craigslist


for what? the tubes i bought 3 months ago?


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## stereo_luver (Oct 30, 2007)

I use Tube Depot most of the time. Audiogon.com for stuff like 300b, 2A4, KT90, KT88 or rare tubes like Telefunken, Ruby, Mullard, JAN......

Chuck


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