Heath ta-16

[roobliz]

There was a thread a few months back about repairing a Heathkit TA-16. I just completed repairing one, here's what I found. TREMOLO/REVERB both were not working. Using the schematic, I found some missing voltages. There was a 13V zener diode installed backwards, reversing it corrected the problem. The LDR was bad in the TREMOLO circuit. I replaced it with a LED and photoresistor(PHOTO) under the chassis where it's nice and dark. The REVERB was out due to some broken wires inside the pan, easy fix! The TREBLE control on the reverb channel was NW, I just followed the wires from the control pot and found a broken solder joint. Look over the whole board for broken solder joints, in total I found 3 more that I'm sure would affect the amps performance. I replaced all the electrolytic caps and now the amp is 100% working!!! Hopefully this helps someone out there...

[Enzo]

Way to go. You never know what you'll find in these, since they were all put together by amateurs from kits

[Mike Patterson]

Parts, please?

Do you have mfr. part nos. for the items you used? I have a TA-16 that I built back in 1968, and have recently refurbished. I would love to have the tremolo working again. Any help and/or advice would be greatly appreciated.

Thanks.

[roobliz]

parts

Mike- The original LDR contains a small bulb and a photoresistor in the sealed package you see on your board. The bulb eventually burns out which causes the failure, the voltage for the bulb part of the LDR is approx 2 volts which is the operating V for most LEDs. I believe any photoresistor will work to turn the sound on/off in relation to the light on/off... Check your local electronics store, both items should be readily available. Good Luck!

[Mike Patterson]

Roobliz,

Thank you for your answer. I do have another question: Did you try to replace the bulb in the original LDR? Would this be possible? I read in a post on Harmony Central where someone said he had replaced the bulb, but the gentleman left no means of contact. I would like to keep the amp as original as possible. TYIA,

Mike

[roobliz]

Hmm... I guess, it would be a tedious procedure though. You'd have to heat up the package to get the bulb out. Finding a working light dependant resistor/bulb package with similar specs could be an option. I think the alternative repair would be the best way to go, the tremolo works very well this way.

These amps have a distinct tone about them, they just sound late 1960's to me.

[Mike Patterson]

Thanks for the info. I was hoping that the LDR case was snapped together, and could be pried apart. I still might try to disassemble it. It will make a good winter project.

My amp has a tendency to fry the power supply diodes every 8-10 years. That, and blowing speakers have been my main problems. I never used the tremolo, so that wasn't an issue when it was my main (read: only) amp. Do you use yours much?

[plott2670]

Heathkit TA-16 Non-Tremoling Tremolo

Allied has a SILONEX part that is listed as a direct replacment for the original Heath opto-coupler:

NSL 32SR3

About $2.50US + shipping.

When I was kid, I made good money putting the TA-16, TA-17 and a few TA-27s together for $50, half what Heathkit charged. Helped pay for my first car!

Blessings!
-charley

[Mike Patterson]

Charley,

Thank you! I didn't know Allied was still in business. That looks like it should work. I'll let you know. Just don't hold your breath, OK?

[Tucker]

Do you happen to know the reverb tank model that Heath sent out with these amp kits, I just found one of these on the side of the road in pretty good working order just without the tank..?

[Mike Patterson]

Do you happen to know the reverb tank model that Heath sent out with these amp kits, I just found one of these on the side of the road in pretty good working order just without the tank..?

Does the amp still have the tank mounting plate screwed in the bottom of the cabinet? I'm not sure of the part #, but it's a long (16-3/4") 2 spring tank.

[wizard 651]

Allied has a SILONEX part that is listed as a direct replacment for the original Heath opto-coupler:

NSL 32SR3

About $2.50US + shipping.

When I was kid, I made good money putting the TA-16, TA-17 and a few TA-27s together for $50, half what Heathkit charged. Helped pay for my first car!

Blessings!
-charley

The allied site shows several silonex optos with very similar ratings. How did you settle on this model as the direct replacement? Not doubting...looking for guidance. really appreciate the info already! saves me a lot of trial and error going thru my bin of photoresistors. Thnx

[wizard 651]

Roobliz's fabbed LED/LDR not a complete fix for my TA-16 trem!

I tried the LED/photoresistor setup. Ingenius and neat. LED flickered and pulsed the audio, sounding like tremolo. Depth and frequency controls work as designed, (LED freq. and intensity respond), but with "intensity" control at zero, the LED stays on, even when trem circuit shorted by footswitch!
Dim, (but lighted) LED, (in what should be the "off" state), attenuates the signal, by reducing LDR resistance, and creating path to ground. Various spec LED's did not change situation.

Following experiments tried without success:

1. Various resistor values in series with LED. Using a Decade resistance box, I increased resistance between LED and trem circuit. Increasing resistance reduced the intesity of the unwanted "off" state residual glow. However, oscillator ceased fluctuating in response to increasing resistance before LED would go completely out.

2. Replaced C29, 30 and 31 in belief they could be shorted or leaking. No change.

3. Tried substituting 8 and 6 volt "grain of wheat" bulbs for LED, (thinking circuit designed around small incandescent bulb, might not be shutting off a low current device like LED). Results: incandescent bulb would not light at all, regardless of control setting.
Bulb did not "stay on" (with the intensity control at zero, like the LED did), but it would not light or flicker with intensity full on, (like the LED would). Final experiment with the bulb: when connected between 13 v. supply for trem circuit, and other bulb lead to a ground, bulb would light up. Also, supply voltage within specs at 13.2 v.

Obvious alternative is to use Silonex direct equivalent as suggested by PLOT2670, (thanks Charlie), but questions remain as to explaining these bizzare results.

Do I have something else defective going on here? Since I have observed the LED flicker and respond to intensity control, showing the circuit works, the xstrs are neither shorted nor open. I can understand that a circuit designed before the LED might exhibit some peculiarities teamed with such a low current device. However, I was surprised that a 6v. 35 ma. incandescent bulb did not funtion at all, (it was the smallest I had on hand).

At this point, my ability to diagnose this is "like a monkey poking at it with a stick"

Any ideas out there? Are the transistors leaking sufficiently to give me unwanted lighting of the LED, yet weak enough that they will not pass enough current to light a conventional bulb?

One last piece of the mystery! Although the LED flickered in response to intensity and rate control, this fluctuation was either non existant or not observable as voltage change on a typical high resistance digital VOM. I would have expected to see some voltage swing or fluctuation.

I CARUMBA,CISCO....WHAT EES GOING ON HERE?

[Tucker]

tank

Thank you Mike,

the plate is there but its blank.

Am I able to use just about any tank with the circuit that's built into the amp?

I am not that interested in the having the thing sound just like every other
TA-16 so can I substitute tanks and to that end anybody know what my limitations are (if any) in terms of choosing one?

[J M Fahey]

Hah !!
I LOVED the little yellow guy in a Mexican hat dancing calypso under the invisible string.
Well, at least that's what it looks like to my none too sharp eyes.
Besides that, congratulations on your restoration project.