[R3SET]

UPDATE: Now working, some other questions here:
http://www.head-fi.org/forums/f7/old...1/#post6065464

Hi there,

I found this old tube amp, it's a Heathkit Daystrom aa-151. This one has probably never been used. There is not even a power plug yet, just bare wire.

There is not much information on the Internet i could find, but it's a build-it yourself kit, probably somewhere from the '60's. The tubes are made in the UK but the Heathkit is from the USA i think?

I've never used a tube amp, and i have some questions for you guys;

- Has this unit been sold here in Europe or has it been imported from the US?
- It's very old, do you think the tubes are all OK? Any steps i have to take before powering it up?
- It's a 117V, with no power plug, so a have to install it to a plug like this:

and than run it trough a 110v->230V adapter i guess? Any problems to expect here?
- I'm now using a Pioneer SX-424 amp (early 70's), will this tube amp sound any better?

This is the unit

 

[joe_cool]

It may be possible to switch or rewire the transformer inside the amp to use 230 VAC. Can you get a picture of the back panel?

 

[Sherwood]

considering the age, it's doubtful that the voltage conversion would be simple (like flick a switch or use a diff't primary simple). The tubes themselves will be fine, so don't worry there. The capacitors may no longer funtion properly, though, so don't get your hopes up too high.

Replacing certain caps is always an option, but it might not be worth it to you, so I'd suggest finding an appropriate voltage converter and having at it!

 

[R3SET]

I found no switch to switch the voltage to 230v. I think i prefer spending 10€ to a converter than to rewire the transformer myself. What happens when the capacitors don't function properly; Will it destroy the amp or only give a distorted sound?

Can i use the tubes for some other amp that comes without tubes (must be cheap) ?

 

[Sherwood]

Looks like this is the tube complement:

Tube complement: 2-6EU7, 2-6AU6, 2-6AN8, 4-EL84/6BQ5, 1-GZ34/5AR4.

You'd surely be able to reuse (or sell) the 6au6, EL84 and 5ar4 -- I don't know anything about the 6eu7 or the 6an8, though. Maybe they're replacements for a more common tube today, maybe not.

If the caps go, the amp won't work. None of them look large, so it shouldn't be hazardous, but it won't function at all if they're shot.

here's some info you might enjoy:
Heathkit Virtual Museum | AA-151

 

[joe_cool]

The 2 output transformers are probably worth more than all the rest put together.

 

[R3SET]

Quote:

Originally Posted by Sherwood /img/forum/go_quote.gif Looks like this is the tube complement: Tube complement: 2-6EU7, 2-6AU6, 2-6AN8, 4-EL84/6BQ5, 1-GZ34/5AR4. You'd surely be able to reuse (or sell) the 6au6, EL84 and 5ar4 -- I don't know anything about the 6eu7 or the 6an8, though. Maybe they're replacements for a more common tube today, maybe not. If the caps go, the amp won't work. None of them look large, so it shouldn't be hazardous, but it won't function at all if they're shot. here's some info you might enjoy: Heathkit Virtual Museum | AA-151

Thanks for the information.

Quote:

Originally Posted by joe_cool /img/forum/go_quote.gif The 2 output transformers are probably worth more than all the rest put together.

haha because of the copper you mean?

So it's a worthless peace of crap not worth investing in

 

[joe_cool]

Quote:

Originally Posted by R3SET /img/forum/go_quote.gif haha because of the copper you mean? So it's a worthless peace of crap not worth investing in

Quite to the contrary, this type of transformer is widely applicable and very expensive to manufacture.

 

[tubes]

You need to use a variac to bring the power up slowly, a quick jolt of juice can blow the caps. Go to audioasylum.com and look under the "vintage" section and "tubes" section, there will be plenty of info on old tube amps. The tubes need to be tested to see if they are still good, if the tubes are bad they should be replaced before powering up. There should be some info on this particular amp at audioasylum.

I would have a technician test the amp before powering up, it may only need a few parts replacing to get it back to spec..

 

[R3SET]

I got the amp working now.

When i use 6ohm, 100W speakers, can i best connect them to 4ohm or 8ohm output?

The sound is very distorted (edit: I think the distortion is only at a specific band of frequenties, it happens with guitars and rock), with lots of cracking when touching the volume-knob. Is that because all the connections are rusted?

Do i need to open it up (how long it had be off off-power to have no dangerous voltages anymore?) and clean it? Are there guides to do this yourself?


Speaker output:

The tubes - they glow very weak but i think they are all working:

110->230v:

 

[fran]

FWIW, that adaptor looks a bit small for an amp of that size. Watch and see does it get hot.

Those tubes will only glow quite weakly. In general, tubes do not glow as brightly as people expect. Most likely the volume pot is dirty and at least needs a clean. Switch cleaner is pretty good for this.

You need to use your ears to tell whether you will use the 4 or 8 ohm connections. No hard and fast rule there.

The distortion is the wost of your problems though. There could be lots of reasons for that, aged capacitors dried out and not longer in spec (very likely), tubes gone bad (although unlikely if the amp has not been used as you say) or if it was a home assemble amp, maybe the fella who did it years ago did not do such a good job. I would try and get some documentation on this amp, instructions maybe a schematic if you can.
There will be high voltages in there that will kill you if you mess about. Thats high voltage DC current where only a few mA are needed to stop your heart. Please be careful. Get someone you know who knows about this stuff to take a look. Its likely an older TV repair guy could help you out.

Fran

 

[Redcarmoose]

Quote:

Originally Posted by tubes /img/forum/go_quote.gif You need to use a variac to bring the power up slowly, a quick jolt of juice can blow the caps. Go to audioasylum.com and look under the "vintage" section and "tubes" section, there will be plenty of info on old tube amps. The tubes need to be tested to see if they are still good, if the tubes are bad they should be replaced before powering up. There should be some info on this particular amp at audioasylum. I would have a technician test the amp before powering up, it may only need a few parts replacing to get it back to spec..

Could not have said it better.


When I am over seas I just get one of those huge voltage converters 220 in 110 out. In the states I use 220 stuff by the reverse way. Really simple but this thing is 15 lbs. Do not drop it on your foot.

 

[R3SET]

Quote:

Originally Posted by fran /img/forum/go_quote.gif FWIW, that adaptor looks a bit small for an amp of that size. Watch and see does it get hot. Those tubes will only glow quite weakly. In general, tubes do not glow as brightly as people expect. Most likely the volume pot is dirty and at least needs a clean. Switch cleaner is pretty good for this. You need to use your ears to tell whether you will use the 4 or 8 ohm connections. No hard and fast rule there. The distortion is the wost of your problems though. There could be lots of reasons for that, aged capacitors dried out and not longer in spec (very likely), tubes gone bad (although unlikely if the amp has not been used as you say) or if it was a home assemble amp, maybe the fella who did it years ago did not do such a good job. I would try and get some documentation on this amp, instructions maybe a schematic if you can. There will be high voltages in there that will kill you if you mess about. Thats high voltage DC current where only a few mA are needed to stop your heart. Please be careful. Get someone you know who knows about this stuff to take a look. Its likely an older TV repair guy could help you out. Fran

The Amp is only 28Watts so it shouldn't be a problem. It does not run hot at all. Sadly the ones over 100Watt are much more expensive, and because i didn't knew the amp was even working at all i chose this one. But it looks like it's working fine.

Indeed, there are lethal voltages inside, and i'm beware of that. I thought maybe all current would be gone after x days leaving it unplugged from the grid. But maybe that's a wrong assumption.

 

[oeyhamre]

Quote:

Indeed, there are lethal voltages inside, and i'm beware of that. I thought maybe all current would be gone after x days leaving it unplugged from the grid. But maybe that's a wrong assumption.

That`s a potentially lethal assumption! Filter capacitors can hold their charge for YEARS if they`re not fitted with a bleeder resistor. Always probe with one hand when on faultfinding missions, keep one hand behind your back or in your pocket. Using a multimeter it`s always wise to measure the voltage across all filter capacitors to make sure there is no charge present before doing any repairs inside the amp. Any remaining charge can be discharged with a modified clip with a 470 ohm 1W resistor in the center. Do not discharge by shorting the capacitor, this might damage the capacitor and/or the wire used to short can melt and/or become welded to the capacitor lug.
If you in any way feel unsure about what you`re doing inside a tube amplifier, then DON`T. Carelessness will get you killed or at best burned!!!

 

[keo]

nice find!

The distortion you're hearing is probably a combination of old caps and oxidation in the controls -- Tube's comment on 9/27 is right on the money, best to do some research before plugging in an old gal like this. audiokarma.org is another good source for information (seems to be down at the moment best to try back tomorrow). Just because you've already plugged it in and nothing has blown up doesn't mean it won't, 30-year old electrolytic caps are hit or miss for being within specifications or completely dead and dangerous to the circuit.