2 channel alternative to A/V receivers

[MikeS 0]

I've made it pretty much to layout and wiring. It should be a good sounding EL-34 PP amplifier provided I don't destroy it......

[JimJ 11]

I've made it pretty much to layout and wiring. It should be a good sounding EL-34 PP amplifier provided I don't destroy it......

Nice

What transformers are those? The logo isn't familiar to me...

What are you using as a line stage?

[MikeS 0]

Peerless. It's a Altec Lansing 345A stereo power amplifier.

Roughly 1959 vintage?

http://www.hifilit.com/hifilit/Altec/1959-d.jpg

I haven't used a tube active linestage in quite some time. Mostly due to time factor, I've been using a vintage SS Harmon Kardon 330B receiver.

When I do listen to a tube amp, I've used the digital volume control in the remote of a mid-tier Pioneer CDP.

While it doesn't fully attenuate the signal, it lowers it enough to feed direct to the amplifier.

Pretty much noise free simple path......but the Pioneer is getting long in the tooth and starting to sound wretched....I may give it some TLC.....

So the other day I went to RS and bought all the 100K stereo pots they had. Out of three I lucked out on one, where it's within 1.5% of each side for tolerance.

So recently, I've been using the 100k stereo pot in a box with RCA jacks. It ain't optimum, but it works pretty good really, provided the cables are shielded and short.

Some day I'd like to invest in a transformer type of volume control from the likes of Intact audio or sumthin'....

The Altec 345A has left and right 100K volume pots right after the input jacks. I'll use some 100K type J Allen Bradley pots I have on hand.

I can just input the CDP direct into the Altec amp.

I do have a bone stock, and I mean bone stock factory wired 1959 Eico HF-85 pre-amp. It sounds ok, but it's a hum monster. I could go through it and modify/restore the unit, and improve upon it, but it's a clean piece of audio history and I don't wanna touch it......Besides, I thought my 6SN7 Aikido linestages sounded better.

Mike

Edited August 25, 2008 by MikeS

[Aaron Clinton 2,372]

Looks pretty sweet, I will watch this topic.

[todd.brust 29]

Nice Amp Mike.

Are these the transformers you were worried about at one point? One had been drilled into?

Either way I figured you have everything working in tip top shape.

[MikeS 0]

Nice Amp Mike.

Are these the transformers you were worried about at one point? One had been drilled into?

Either way I figured you have everything working in tip top shape.

Yeah, the PS transformer has a 1/4" diameter by 1/8" deep hole drilled in the lamination stack on the bottom.

This was from a repair job. The amp had undergone some thermal stress at one time, and I don't know how or why.

It cooked the 250 ohm dropping resistor for the screens of EL-34, going ablaze. It wiped out the insulation on the 5 volt heaters for the rectifier tubes, and part of the 6.3 volt winding for the signal and output tubes.

The repair was to fix the burnt resistor. The imbecile broke out the black and decker with the 1/4" bit to drill out the tag strip that the resistor was mounted to,(underneath the PS xformer)and power rammed it through the chassis and into the lamination stack.

Then he mounted a new tag strip and resistor between the rectifier tubes, drilling another hole in the chassis.

I tore the PS xformer down. It did undergo a bit of stress, with some wax melted, but not too bad.

I then removed the burnt insulation on the heater leads, and replaced the insulation. Once assembled, I measured for DCR, and then measured AC with the xformer unloaded.

DCR #'s for the PS xformer are right in spec with the Sams photofacts for Altec 345A. (I never really trust sams phonyfacts, but it did make me feel a bit more confident.)

AC voltage unloaded on the secondary is a bit higher, but it's for 117 volts in. Where I was measuring at 120 volts in. That's my wall voltage, so I gotta go from that.

I then ran the PS xformer for around 7-8 hours unloaded. 120 volts AC, with the secondary and heater leads taped-off, floating.

A wore out power supply xformer running unloaded with say a few shorted windings will heat up. Some may start to buzz, even more so if the input voltage is exceeded a bit.

But this Peerless xformer is big beast, and probably rated pretty well and would take a bit more abuse.

After 7-8 hours, it got mildly warm unloaded.....I'll see how it does with a load.

The only other PS xformer I have that is larger, is a Masco 6550 PP PA amp. The PS xformer is a big ol' 20-25 pound monster. Even the big old tube television PS xformer's don't even come close.

One output transformer was in good shape, the other had got rather hot at one time. Hot enough to shift the lamination stack crooked. I disassembled both OPT's, one looked fine.

The other I took to work and heated the OPT in a electric oven. Once warm enough, I re-aligned the lamination stack straight. It worked well, and the whole place reeked like wax...heh

I put them back together and measured the DCR numbers, they are still close enough. They won't be exact I suppose. I measured both OPT's with a sig gen using square waves with a simulated load for the primary, and a dummy load for the 8 ohm secondary tap. Shorted windings would show peaks and quick drops in the square wave response around midband. I didn't see it, and response between the two was quite similiar.

I bought it from some old timer in his '90's. He's the first owner. I doubt he had turned this amp on in 30 years or better. Who knows.......but it was a den and a latrine for a mouse for quite some time, the chassis was trashed.

It was a real basket case to be honest.

Edited August 25, 2008 by MikeS

[MikeS 0]

If this place hadn't went tits up years ago, I could just take it down there and complain........

[todd.brust 29]

Sounds like you went through a bunch of trouble with those transformers.

Are you just waiting on parts to do all the wiring?

[MikeS 0]

Sounds like you went through a bunch of trouble with those transformers.

Are you just waiting on parts to do all the wiring?

Yeah, the transformers were kind of a pain in the ass. But they are Peerless. Peerless was a well respected transformer company in the tube heyday, especially when it came to audio related products.

Well engineered.

Look at this way......a retired EE who is around 72-73, and a audio buff for 50 years, mentioned that the amp is probably a keeper once he knew it had Peerless OPT's.

A local retired audio engineer who is in his 60's, asked if the amp had Peerless iron. And then got a grin on his face when I said it did.

The specs in the operating instructions claim 40 watts RMS continuous each channel at less the 1/2% THD @ 40-15kHz.

100 watts peak per channel. Even at 40 wpc RMS, I still think that's crowding the amp kinda hard......who knows, it's 1959 measurements. I doubt I'll listen to more than 20 watts per side without getting blasted...more like 10....

Frequency response + or - 1db, 10Hz-100kHz. It takes a rather tightly coupled, (wound) output transformer with a good size core to get those numbers. I have no idea what wattage those measurements were made at.

I'm working on the amp now. I have all the parts, except four 5k trimpots, and four 10 ohm 5 watt current sensing resistors.

[todd.brust 29]

Keep this log updated then. I always enjoy seeing your work.

You said that you disassembled the OPTs correct? Do you have any pictures of that? I still have yet to see how they wind everything inside of a transformer.

[MikeS 0]

Dunno what's wrong with photobucket...............

I didn't unwind the xformers, I just pulled the end caps to inspect them and repair the insulation damage to the PS heater windings.

My old retired EE buddy has unwound, gapped and done interesting things with transformers, but it's way beyond my scope and capability.

I'd end up with a pile of scrap copper/iron and paper.

I got a Radio Designers handbook that explains how to wind xformers and theory/math, etc......but it is real deep for my peanut brain without learning some math.

OPT2

OPT

The first one appears to be discolored from heat stress. But I don't think it is. The OPT's are not consecutive in the part numbers. One may have been from a different run.

You can see how the wax had gotten hot.

PS

Heater winding insulation damage.

Edited August 29, 2008 by MikeS

[MikeS 0]

.

Edited September 3, 2008 by MikeS

[todd.brust 29]

That is so clean!

Makes me want to start with a clean chassis and rewire everything!

Maybe it's time for a new project.

But looking great Mike! How much more do you have left?

[MikeS 0]

Heaters are done.

B+ for the OPT's is almost done.

I'm working the screen de-coupling circuit as well.

Then the B+/de-coupling/filtering sections for 6C4 and 6AU6.

I can then start pondering and wiring out the negative bias circuit. (still need them 5K trimpots and 10 ohm R's)

From there, I can probably go ahead and wire up the coupling/DC blocking caps and the rest of the signal circuit, and then wire in the input signal leads and the volume pots.

I also still need to hook up the power supply grounds, and signal grounds as well.

And then wire in the power cord and power switch. I still need to drill some holes and mount binding posts and the back panel.

That's all I can think of at the moment.....

I won't take too long now that I'm actually wiring and laying the circuit out.........but I am slow....

[MikeS 0]

I messed up the link to the last photo....

Edited September 4, 2008 by MikeS

[MikeS 0]

Edited September 9, 2008 by MikeS

[todd.brust 29]

Moving along.

Just an OT question but did you ever get Eico St-70 working?

[MikeS 0]

No Todd, I never did get the Eico ST-70 to work properly. The very first time it did work, but I had the 6SN7's connected wrong which yielded literally no gain and real distorted output.

Then when I did connect the 6SN7's right, I ended up with a major midband oscillator.

I rebuilt the amplifier, with some mods sourced off the internet. I thought maybe the modifications were contributing to the amp going into positive feedback, and then converted the amplifier into a straight power amp hoping the positive feedback issue would go away. It didn't......

I used speakers for load, and it would really scream with positive feedback. I had a couple guinea pigs at the time in the room. It would put them into serious launch mode......one would shoot a foot straight up, and then do about 30 laps in it's cage within 2 milliseconds......they hated it.......so do I........I need to buy some load resistors from PE.

If the Altec amplifier turns out to be a stable circuit, and I don't end up troubleshooting the thing, I can go ahead and return back to the Eico ST-70 and start troublshooting that amp.

I need the load resistors for both amplifiers to do proper bench testing troubleshooting. I got the scope, the probes, the half-assed signal generator......I just need the load resistors.....

I need to chase out what section of the circuit is causing/going into positive feedback, using a scope will help.

It could be a bad capacitor can, a scope will help chase that out.

And I'm the learning curve when it comes to bench testing amplifiers/troubleshooting.....I'll finger it out.....

I still need to buy the R's and trimpots, but I'm getting pretty close to having this Altec amp finished.

Edited September 24, 2008 by MikeS

[todd.brust 29]

No Todd, I never did get the Eico ST-70 to work properly. The very first time it did work, but I had the 6SN7's connected wrong which yielded literally no gain and real distorted output.

Then when I did connect the 6SN7's right, I ended up with a major midband oscillator.

I rebuilt the amplifier, with some mods sourced off the internet. I thought maybe the modifications were contributing to the amp going into positive feedback, and then converted the amplifier into a straight power amp hoping the positive feedback issue would go away. It didn't......

I used speakers for load, and it would really scream with positive feedback. I had a couple guinea pigs at the time in the room. It would put them into serious launch mode......one would shoot a foot straight up, and then do about 30 laps in it's cage within 2 milliseconds......they hated it.......so do I........I need to buy some load resistors from PE.

If the Altec amplifier turns out to be a stable circuit, and I don't end up troubleshooting the thing, I can go ahead and return back to the Eico ST-70 and start troublshooting that amp.

I need the load resistors for both amplifiers to do proper bench testing troubleshooting. I got the scope, the probes, the half-assed signal generator......I just need the load resistors.....

I need to chase out what section of the circuit is causing/going into positive feedback, using a scope will help.

It could be a bad capacitor can, a scope will help chase that out.

And I'm the learning curve when it comes to bench testing amplifiers/troubleshooting.....I'll finger it out.....

I still need to buy the R's and trimpots, but I'm getting pretty close to having this Altec amp finished.

Lol at the guinea pigs. I don't know why I thought that was funny.

Your amps are always laid out so no nicely. Want to re-do some wiring in my heathkit?

Can't wait to see the finished Altec!

[MikeS 0]

Edited November 20, 2008 by MikeS

[todd.brust 29]

this is great!

Now the question, how does it sound?

[MikeS 0]

The amp works........

[todd.brust 29]

Nice!

Unfortunately, the guy who owned the local Hi-Fi passed away a couple weeks ago. I may end up picking up a few things before the fmaily closes shop.

He has some nice project pieces, so I might be starting a rebuild soon!

I wish I could get his HK Citation 2 he had sitting around. That thing was a beast of an amplifier.

[MikeS 0]

Nice!

Unfortunately, the guy who owned the local Hi-Fi passed away a couple weeks ago. I may end up picking up a few things before the fmaily closes shop.

He has some nice project pieces, so I might be starting a rebuild soon!

I wish I could get his HK Citation 2 he had sitting around. That thing was a beast of an amplifier.

That sucks. Sorry to hear that Todd. Those old timers pass on, and another little bit of the old school knowledge disappears along with it.

Yeah, I'd be trying to glom on to whatever you can afford/get your hands on.

Along with projects, maybe see what he has in the way of test gear. Old school volt ohm meters, VTVM's, tube testers and tubes are things to snag.

What happened to the Harmon Kardon Citation II amplifier? Did it pretty much vanish right when he passed away? That's a well coveted amplifier, and worth a few bucks as well.

I hooked the Altec 345A amplifier up to my LaScalas just about a hour ago. Plenty of power, and bass is strong.

It has new tubes except for the 5U4 rectifiers, and brand new parts. So it will take some time for the amp to settle-in. It still sounds rather good, however. Just a wee bit bright/weedy......and I'm pretty sure it's the new parts and EL-34's. Time will tell I suppose....

I listened to it about 20-30 minutes just to hear it. Now it's back to the bench for testing/checking/measuring on the scope.

[todd.brust 29]

He had lots of test equipment. That would be something useful for me.

As far as I know, the Citation II is still sitting on top of his piano in the shop. That thing is a beast of an amp. Lots of Iron in that. He had all oft he original literature with it. He showed it all to me. He even had all the newsletters that got sent to citation owners. Very cool stuff.

I want some tube amps to run my Dahlquists. maybe 60 watts per side. Either a set of monoblocks or a 2 channel. I have been on the lookout for a while but everything is out of my range(I'm still broke)