Category Archives: Heathkit

Heathkit Projects, Restorations or Modifications.

Repairing VTVM Pilot Light

Lurid Red of the new Pilot Lamp
Lurid Red of the New Pilot Lamp

I found a great solution to old tape used in the Heathkit VTVMs for the RED pilot lamp. The lamp is just a #47 bulb, shining through a hole in the top of the meter face. The tape isn’t mentioned in the instructions, so perhaps it was pre-installed in the back of the meter face.

 

 

A Cheap Fix
Also Useful for Repairing Antique Pilot Lamp Film

 

In any case, this tape sometimes falls off or is nearly falling off after 50 years. It also fades and loses it’s reddish glow. An excellent solution was found in the form of a red-neck repair from the auto parts aisle of Walmart: Tail Light Repair Tape, US$2.00.

Tape replaces old, crinkly, peeling tape from this spot.

 

 

 

Above: Below the roll of red, translucent tape, the old pilot lamp film and the new piece cut to replace it.

Left: Adhesive is sticky and the new piece goes over the hole in the meter through which the pilot lamp shines.

An Improved VTVM Battery Eliminator

One of the disheartening things about buying an older (…well, they’re ALL older, now…) VTVM is opening it up and finding either an old, leaky battery, or evidence of one. This usually damages or destroys the battery contacts and sometimes also the circuit board. The battery, usually a standard 1.5V C-cell, is necessary for measuring resistances with the ‘ohms’ scale.

A great improvement has been suggested over the past couple of years to replace the battery entirely, using a modern voltage regulator, drawing power from the filament circuit. A version of this has been available on several Heathkit lists and I’ve used it in my V-7A and IM-18. This replaces the battery and removes the risk of leakage.

More recently, Peter Bertini, Pop Comm Magazine (and others) have pointed out that the circuit used an inefficient half-wave rectifier, probably adding stress to the (already old) VTVM’s transformer.

If, in ‘ohms’ mode, the probes are touched together (0.0 ohms resistance), the entire 1.55 Volts is placed across a 9.1Ω resistor, resulting in the maximum current draw of (I=V/R), or 1.55/9.1 = 170ma. This doesn’t count diode loss and heat loss in the voltage regulator.

The following circuit attempts to repair the inefficiencies and addresses ripple filtering in the regulator, so as to provide an efficient and accurate VTVM Battery Eliminator.

An Improved VTVM Battery Eliminator

The input is from the 6.3VAC filament circuit. The output goes to the same locations as the original dry-cell battery.

In the case of a Heathkit V-7A, is grounded, with +1.55VDC at the ‘free end’ of the 9.1Ω resistor (see a schematic at http://www.heathkit.nu/heathkit_nu_V-7A.html).

VTVM Battery Eliminator, Grounded
VTVM Battery Eliminator, Grounded

Overcurrent Issues

The transformers in these VTVM’s are barely capable of lighting the two vacuum tubes. Is it possible that the addition of a ‘battery eliminator’ for the Ohms measurement could cause a problem?

While converting a Knight-Kit KG-620 for battery-free operation, I was able to measure the current draw. Instead of an LM317 (1.5A) regulator, I substituted an LM317L – 100mz, current-limited regulator.

Idle current is measured around 5 ma and peak current at around 95 ma with shorted terminals, and range switch to Rx1. Current limiting would probably curtail measurements on the low-end (below 100 ohms).

A second way to address current draw is as follows: the KG-620 has a Type #47 pilot lamp, drawing 150ma. Replacing this with a LED will reduce the lamp current by 10x from 150ma to around 15ma. This effectively ‘recovers’ any current used by the battery eliminator.

This would also work for the Heathkit V-7A and IM-18 (and variants) as the pilot lamp is also a 6.3V, Type #47 lamp across the filament supply. Added benefits: a) reduced heat, b) reduced transformer load, c) never have to replace the pilot lamp again.

 

References

  1. Peter Bertini, “Fixing Up A Vintage Heath IM-13 VTVM”, Popular Communications, March 2010.
  2. AntiqueRadios.com, forums – Search “VTVM battery draw…”
  3. LM117/LM317A/LM317 3-Terminal Adjustable Regulator (Datasheet), National Semiconductor
  4. 3-Terminal Regulator is Adjustable (Application Note 181), National Semiconductor, Figure 2. Adjustable Regulator with Improved Ripple Rejection.
  5. The V.T.V.M.: How it Works, How to Use it , Rhys Samuel, Gernsback Library 1956.
  6. Servicing Radio and Television with a Vacuum-Tube Voltmeter, an excellent, 1951 document from Sylvania Electric Products.
  7. AD5X’s method of turning Type 47 Lamps into LED Lamps, saving heat & current

“Most Accurate” SB-630 – An Update of an Old “Timer&”

Or, “Most Accurate” SB-630: Retro Style Desk Accessory, Updated on a Budget

A while back, I was given an SB-630 Station Console by an old timer acquaintance.

The SB-630 is a nice, but not especially necessary station accessory. Some hams built them just to have the complete SB-line. The console consists of a passive SWR meter, a phone patch, a motorized Digital Clock and the unique feature: a 10-minute Identification Timer. Better versions of the SWR Meter and Phone Patch were sold separately; the clock-timer was unique, so the SB-630 was merely an opportunity to wrap them all up in a single desktop accessory. Since there’s nothing unique about the SWR Meter or the Phone Patch, for my purposes, I shall focus on the clock-timer combination.

My plan was to build a new clock display, keeping some of the old style (albeit 1970’s style, not 60’s), and drive them with an Arduino micro controller. The real-time clock is provided by a Maxim DS1307 (formerly Dallas Semiconductor) 8-pin IC. The chip is tiny, uses very little current when it’s ‘on’, and is backed up (according to the datasheet for 10 years!) by a single CR2032 3-volt lithium battery.

The LCD is from SparkFun, a Red-on-Black, Backlit LCD which fits well.

Construction

All Tubes and the Plate-Filament transformer were removed (and saved, for future tube projects). The clock was given to a local collector who prefers to keep his Heathkits original. The functionality replaced – and enhanced – by adding a Real-Time Clock (RTC) chip, a WWVB receiver and Arduino code to interpret the 1950’s era clock signal.

The WWVB receiver reads each ‘pulse’ of the signal and interrupts the Arduino (INT1) to add the ‘tick’ to the buffer. Once the whole signal is received, it can be interpreted as a date and time. The RTC pulses (INT0) each second in order to drive the display clock.

In addition, an LM35 sensor provides the current room temperature.

Original WWVB decode source from http://duinolab.blogspot.com/2009/06/arduino-cmmr-6p-60-almost-accurate.html (Capt Tagon) and all others who’ve improved this code. Website seems abandoned, but the source code is good. My alteration is to remove the timer interrupt (1000 times a second) which operates the 1-second tick and replace it with the square wave output (SQWE) signal from the RTC chip, a Maxim DS1307.

The LCD is 16×2, and the layout needs to accommodate Date, Time, and Day, along with an ID Timer. A room temperature indicator is ‘extra’.

SB-630 LCD Layout
Character Display is laid out on the 16×2 LCD Display.

It’s a bit cramped, but I’m able to show everything I wanted to display, and I have plenty of Arduino pins left to trigger the ‘IDENTIFY’ lamps and ‘audio tone’, and a few pins left for future expansion.

Schematics

The DS1307 has it’s own battery-backup, which retains the time on power-off.

DS1307 schematic
Detail of the DS1307 Real-Time Clock connections.
Schematic of the CMMR-6P-60
Schematic of the CMMR-6P-60 (now unavailable)
Overall Schematic of the Microcontroller
Overall Schematic of the ATMEGA168 IC and it’s connections.

 

The WWVB Receiver IC is no longer available. A better choice today would be a GPS receiver, which would provide the same (or better) accuracy and is in the same price range now, with some GPS modules selling for as little as US$14.

Finally, the ATMEGA168,  LCD, ID Lamp Relay, Temperature Sensor, and the Tie-in with Original Switches.

Code

Source Code contains classes for the DS1307 and the CMMR-6 WWVB receiver.

 

Heathkit HW-101

The <a href=”http://mikeyancey.com/HW-101_refurb.php”>HW-101</a> refurb is now complete. This seemed like an extensive redo, but was not, because many of the boards went mostly untouched. It began with a redo of the HP-23 power supply with an HP-23RL board from The Heathkit Shop. And it ended with replacement of two of the Carrier Oscillator crystals, which with age had changed too much to adjust with serial or parallel capacitance.

For kits anyway, this was the pinnacle – the tip-top. No one would ever make a 20-vacuum tube transceiver again.

Heathkit IG-102, Solid State Edition

I’d recently heard about a conversion of a tube Signal Generator to Solid State. I found the original article in a great old book called ’99 Test Equipment Projects You Can Build’, by 73 Magazine. I snagged the book from eBay for only $2.00 (plus shipping). My copy is a small hardback, red cover. Print’s kinda small.

Same article mentions adding a three-range (10khz, 1mhz, 10mhz) crystal calibrator on-board (since you now have boatloads of room inside without the tubes and the transformer).

Each ‘half’ of both tubes is replaced with a FET Pin numbers are mentioned, so you go underneath (unfortunately sticking the leads in the tube socket holes won’t work…) and solder a FET lead to a Socket Hole. I think there’s one socket hole (besides the filaments) that remains unconnected.

I’ve written on the schematic which FETs appear to work. I settled on MPF-102s, although I tested a couple of versions. The book project specifies four 2N5951’s.

An IG-102 FET Conversion Schematic

There are two resistor changes (actually mods) due to the lowered voltages:
Solder a 75 ohm resistor across the existing 33k (see left of ‘BF Front View’ switch.
Solder a 90 ohm resistor across the existing 4.7k (see above V2A 1/2 6AN8). On some models the existing resistor may be a 10k.

There are no other changes other than what’s marked at bottom of the schematic (removing the cord and power supply. Replace w/9V battery. I also did the fancy LED thing. Nice to know if it’s ON so you don’t run down the battery.

I also added a ‘wall wart’ plug for outside power. Fancy.

IG-102 FET Version – Tinkering with Tubes

I’d recently heard about a conversion of a tube Signal Generator to Solid State. I found the original article in a great old book called ’99 Test Equipment Projects You Can Build’, by 73 Magazine. I snagged the book from eBay for only $2.00 (plus shipping). My copy is a small hardback, red cover. Print’s kinda small.

Same article mentions adding a three-range (10khz, 1mhz, 10mhz) crystal calibrator on-board (since you now have boatloads of room inside without the tubes and the transformer).

Each ‘half’ of both tubes is replaced with a FET Pin numbers are mentioned, so you go underneath (unfortunately sticking the leads in the tube socket holes won’t work…) and solder a FET lead to a Socket Hole. I think there’s one socket hole (besides the filaments) that remains unconnected.

I’ve written on the schematic which FETs appear to work. I settled on MPF-102s, although I tested a couple of versions. The book project specifies four 2N5951’s.

IG-102 - FET
Schematic for the FET version of the Heathkit IG-102

There are two resistor changes (actually mods) due to the lowered voltages:
Solder a 75 ohm resistor across the existing 33k (see left of ‘BF Front View’ switch.
Solder a 90 ohm resistor across the existing 4.7k (see above V2A 1/2 6AN8). On some models the existing resistor may be a 10k.

There are no other changes other than what’s marked at bottom of the schematic (removing the cord and power supply. Replace w/9V battery. I also did the fancy LED thing. Nice to know if it’s ON so you don’t run down the battery.

I also added a ‘wall wart’ plug for outside power. Fancy.