Heathkit tube tuners?

[DKak]

All,

Dyna seems to own the "mindshare market" on vintage cheap tube tuners, but what about Heath's products?

Two of the tuners in my collection are a Heathkit AJ-12 FM Stereo tuner and a Heathkit AJ-41 AM/FM Stereo tuner. Both were introduced in 1964 and are all tube except for the rectifiers -- they're early '60s silicon diodes.

These models have the brown leatherette and chrome "'57 Chevy" styling, which to me looks really cool. At least Heath took a styling risk. And both of these are in very nice physical shape. If you look here, you can find pictures of both: http://www.qsl.net/kb7rgg/heath/products/audio.html

I had the AJ-12 aligned recently and it sounds pretty darn good, but a little noisy. Just a little, though. Still has all original tubes, each still around 60-65% of new values. I suspect retubing and then realigning might be a worthwhile investment. I believe I can still find all the tubes in NOS form.

The AJ-41 needs some restoration work...it wasn't treated so well by its previous owner(s). But the case, faceplate and chassis are in good shape.

I do have the construction/instruction manuals for both.

I don't plan to sell these, but I'm torn regarding possible "modernization" projects. Original vs. old design with new parts. What to do? I could use nice Cree high voltage Schottky or Fairchild Stealth diodes as a very basic and nearly invisible change, but I could go further and modernize the caps and resistors in the audio path, too, for a possibly bigger change. Either way the tuners would no longer be stock, but they'd most likely be improved.

How much improvement does anybody guess I'd get by upgrading the diodes? It seems to me that much newer and better silicon there might be a big improvement.

Anyone have any pro/con thoughts on this whole thing? Heck, I don't even know how well these were regarded in their day. The Dyna FM3 seems to keep everyone's attention in cheap tuners of the day. Again, I'm not considering selling them, so resale value isn't a big factor. Just wondering if others think the effort might pay off with a lot better performance? If so, how much better would you estimate, and where should the money go toward improvements?

Thanks --

[bob adams]

I don't know anything about tube tuners but my thought on it is I wouldn't modify or upgrade the tuners in any way. I would replace any tubes or components that were weak or had failed and have the tuners aligned. Bring them back to as new as possible specs and then enjoy them for what they are. There are a ton of SS analog and digital tuners you can upgrade and "hotrod". And the tube tuners are probably worth more if left stock.

As an aside I would love it if someone knowledgeable in tube tuners would start a thread in here. I want one but don't know enough to decide which brand or type(?) I should buy. It would be great to have a tube tuner guru to ask.

[mhardy6647]

Can't beat the Sherwood tube units for sound quality per $ IMNSHO.

The Heathkits aren't particularly valuable as collector's items... replacing caps in the audio path is reputed to be a Good Thing. "Punker X" is the local tuner expert.

I have one of the Heathkit orange-cabinet tube AM-FM tuners... I forget the model number. AJ-41, maybe (i.e., same as above)? With meters rather than magic eyes.

[DKak]

I have one of the Heathkit orange-cabinet tube AM-FM tuners... I forget the model number. AJ-41, maybe (i.e., same as above)? With meters rather than magic eyes.

Sounds like an AJ-41. See the website I referenced above for pix.

I have a pile of SS tuners, some very, very good. Two are at Punker's now: a Marantz 2130 and a Sansui TU-9900. Getting full blown resorations with a full audio path upgrade.

I just thought it would be nice to take the humble Heath and try to make it something special. Don't know that they'll ever be worth anything as collectables, so this is why I'm considering modernizing them to make them sound the very best they can.

As I mentioned in the earlier post, aside from a little noise, the little AJ-12 has tube magic. It is surprisingly sensitive, although I have an APS-9 antenna and a Magnum 205 Signal Sleuth feeding it.

I still wonder about those rectifiers. Tube rectification can be so sweet, but that's not really possible here. Just thought it might be worth trying the very best of today's SS diodes. Of course, that's what led to thinking about taking the mods further.

[bob adams]

Reading on one of the yahoo group sites there seems to be people who do mod these old tube tuners (at least the Dynacos). See the posts starting at #929. Here's a link.

http://groups.yahoo.com/group/diy_audio_tweaks/messages

[bills]

I still wonder about those rectifiers. Tube rectification can be so sweet, but that's not really possible here. Just thought it might be worth trying the very best of today's SS diodes. Of course, that's what led to thinking about taking the mods further.

i don't understand how any one could hear the difference between solid state
or tube rectification .
could we also hear the difference between full wave and half wave?
do you think that maybe we are carrying this tube stuff a little too far?

bill

[3Guncolor]

Maby tube rectification in a power amp may make a difference. But I would say in a tuner all it will do is burn power and make heat. I would want good filters and no hum in a tuner. To me the best way is to leave it the way it was first made and replace needed parts.

[bills]

huh?

[3Guncolor]

I guess what I should have said is using tube rectification in a tuner will just use more power then using solid state. I would not change it from tube to soild state if it was made that way unless there was good reason to. But I would never go from solid state and change it to tube . Hum is more of a factor in a tuner or preamp. Full wave has less chance of hum.
In a power amp it may sound better to use tube rectification but I can't tell the difference.

[mhardy6647]

Here's a cheap and cheerful way to evaluate the tube vs. ss power supply question. Get a Heathkit 400V bench power supply, bypass the on-board P/S in the tuner and run it off the outboard, tube/regulated P/S. If it sounds better... build a simple CRC or CLC tube P/S on an external chassis and plumb it into the tuner with an umbilical cord. You don't need real HV or current, so it should be a simple and relatively inexpensive P/S to implement.

EDIT: An example of the P/S I am referring to is the Heathkit IP-17:
http://www.angelfire.com/electronic/funwithtubes/images/Heathkit_Power_Supply.jpg

[Chad Hauris]

There is no difference in the DC that a tube or solid state recitifier puts out...the tube rectifiers do have higher voltage drop and thus there would be less output voltage. If you are experimenting with using different types of rectifiers the change in voltage drop is what would change the sound of the device.

Theoretically silicon diodes can produce RF noise when they operate whereas tube don't but I have not really observed this in operation. There are sometimes ceramic capacitors shunted across silicon diodes to supress this noise.

[goldear]

There is no difference in the DC that a tube or solid state recitifier puts out...the tube rectifiers do have higher voltage drop and thus there would be less output voltage.
I used to believe this too. But, I don't any longer. You are correct about the larger voltage drop on a tube rectifier. But the tube rectifier also has much higher internal resistance. This means that the tube circuit will have poorer voltage regulation as a function of load, than will a SS rectified PS.

But there is another difference that has come to be recognized in more recent years: Tube rectifiers have less switching noise, than do transistors (I'm not counting those mercury rectifiers, which are a whole different ball game).

This is caused by the recover time that it takes the recitifier diode to switch from on to off. Some very fancy SS rectifiers are not available that address this. These are Hexfred rectifiers, and Shotkey diodes. Both have considerably less switching noise that they emit than do traditional silicon rectifiers. Many people claim that these can make an improvement in the sound. I have yet to try any of these fancy diodes myself, so these are third-hand reports that I cannot confirm as yet, due to a lack of personal experience.

I am planning to try switching out some of my SS rectifiers in some of my equipment one of these days to see if I can hear any improvement from the Hexfreds, but I have yet to get around to it.

[mhardy6647]

Aye, matey... the 'sag' in the unregulated tube P/S is probably part of its charm.