Heathkit IP-17 (1968–1977)

A restyled bench supply that powered a generation of tube projects. It still does, if you can find one that hasn't been cooked.

Overview

The IP-17 is a regulated high-voltage bench power supply. It's the kind of unglamorous instrument nobody photographs, but every tube builder of a certain vintage owned one or knew someone who did. It measures 13-3/8"W x 11-1/4"D x 5-1/2"H in a low-profile cabinet. It descends directly from the PS-4, which Heathkit introduced in the late 1950s and which formed the circuit basis for the IP-32, the IP-17, and later the IP-2717. Only styling and minor circuit changes separate the whole run.

The headline numbers are simple: 0-400 VDC at 100 mA on the B+ output, a negative bias supply of 0 to −100 V at 1 mA, and 6.3 VAC at 4.0A for filaments. The 100 mA figure is continuous, with 125 mA available intermittently. That matters if you're running a pair of 6L6s or a small push-pull stage. Two meters let you watch output voltage and B+ current draw at the same time. The voltage meter reads either B+ (0 to +400 V) or C− (0 to −150 V), depending on the position of a meter switch. That dual-meter arrangement is one of the reasons the IP-17 stayed in catalogs for a decade. You can see the current climbing as a tube starts to red-plate.

The IP-17 came out in 1967, too late for Heathkit's main catalog that year. It sold for $59.95 in kit form or $89.95 factory-wired as the IPW-17. In 1977 it was replaced by the nearly identical IP-2717, which carried only minor styling changes - mostly colors - and a higher price of $109.95 as a kit, $210 factory-wired. That version soldiered on into the mid-eighties before being phased out without a direct replacement.

The differences from its predecessors are mostly details. The selenium screen rectifiers of the earlier IP-32 were replaced with silicon diodes. The transformers were updated so the unit could be wired for either 120 or 240 volt operation, and a three-wire AC plug was added. A third pole went onto the meter switch, and two neon lamps indicate whether the voltmeter is reading C− or B+ volts. That's a small thing, but it prevents the kind of mistake that lets the magic smoke out of whatever is on the bench. The 6.3 or 12.6 VAC heater supply is available for external heaters at a total load of 25 VA, which gives some flexibility with tube types beyond the usual 6-volt crowd.

The circuit breaks down into seven functional blocks: filament power, the negative/bias supply, the B+ supply, a screen supply for the regulator tubes, a control circuit, the series regulator, and the metering circuit. It uses six tubes - two 0A2 150 V regulator tubes, a 6BH6 control amplifier, a 6X4 bias rectifier, and two 6L6 series regulator tubes - along with six silicon rectifier diodes. The current meter is a 150 mA full-scale unit with a series resistance of 0.66 ohms, placed in line with the B+ output. There's no provision to monitor C− output current, since it's very low and internally current-limited. The voltage metering uses a 1 mA meter with switched series resistors: R25 at 150 K for the C− range and R24 at 400 K for B+.

If you're shopping for one, the PS-4 lineage running through the IP-32, IP-17, and IP-2717 is worth understanding. The design is well-documented, and because the same basic circuit appeared in four models over roughly twenty-five years, parts and knowledge are shared across the family. The 6L6 pass tubes are still plentiful, the 0A2 regulators are common, and the 6BH6 and 6X4 are not difficult to source. The transformers are the weak point in any old Heathkit supply, as they are in most tube gear of the era. The IP-17's separate filament and power transformer arrangement, inherited from the PS-4, is at least a sensible design.

Period coverage of the IP-17 is thin in the usual audio magazines. This is test equipment, not a receiver or amplifier, and the audio press of the late '60s had little reason to review a bench supply. The most useful contemporary documentation comes from Heathkit's own catalogs and from DB-Magazine (December 1967, p.9), which described the new instrument look Heath introduced. It had a cabinet frame of front and rear panels and side rails supporting the chassis independently of the top and bottom shells, with retractable carrying handles concealed in the side rails and a die-cast front panel bezel in chrome and black over beige panels and cabinet shells. The IP-17 is a product of that design, and the unit looks more purposeful than the earlier PS-series supplies.

The table of Heathkit power supply current ratings shows the PS-2 and PS-3 delivering considerably less current at the voltages most tube projects actually use - 15 mA and 20 mA respectively at 400 V, versus the IP-17's 100 mA continuous. Even at 200 V, where the PS-2 could manage 130 mA, the IP-17 still holds its 100 mA figure. That flat current capability across the voltage range comes from the PS-4 redesign, which separated the filament and power transformers and used a tube lineup that allowed current output independent of the voltage setting.

On the used market, IP-17s turn up with some regularity, and the going rate for a working example has historically been modest. The Audio-Express (September 2004, p.68) coverage of a supply rebuild project noted that these units routinely show up on eBay for around $30 or so, and suggested the Eico and Lambda high-voltage supplies as alternatives if an IP-17 couldn't be found. That was written in 2004, and prices have drifted since, but the IP-17 has never been a collector's item the way a Marantz receiver or a McIntosh amp is. It's a tool, and it's priced like one. A working IP-17 is one of the cheapest ways to get a useful regulated high-voltage bench supply, and the rebuild path - recapping, checking the pass tubes, verifying the meter calibration - is well-trodden.

The Audio-Express piece also noted that the modular circuit boards in the IP-17 sit on a saddle that makes replacement straightforward. The new boards fit right into the saddle, and swapping them is a simple matter of snipping connections, removing the saddle, and drilling out the old mounting points. The circuit is documented, the layout is accessible, and the whole thing was designed to be assembled by a hobbyist in the first place, so it can also be taken apart and put back together.

The IP-17 isn't a piece you buy for its looks or its rarity. You buy it to run a 6L6 push-pull amp on the bench, check the bias on a vintage receiver, or bring up a tube project slowly on a variac without guessing at the voltages. It does that with two meters, a well-understood circuit, and a modest price.