HP 6209B High Voltage Supply (320V at 1A), teardown and repair. - Page 1
Forum section: electronics / testgear

author: anotherlin
author_rank: Frequent Contributor
timestamp: January 20, 2015, 01:41:14 pm
content: Hi everyone,Just scored a "for parts or repair" HP 6209B High voltage power supply. In fact, I already scored a fully functional one about a year ago (https://www.eevblog.com/forum/testgear/hp-%28harrison%29-6209b-hv-supply-%28320v-at-0-1a%29/), but that was an older revision, which was even branded as HP Harrison. This repair would a good opportunity for a teardown/analysis of the supply. It uses through hole parts, replacements are easy to find, and operating/service manual is readily available (http://www.keysight.com/en/pd-1000001527%3Aepsg%3Apro-pn-6209B/single-output-power-supply-0-320-vdc)The 6209B is a very interesting power supply. It is a high voltage supply (320V) which is not that common, it was probably intended for use with tube design. I personaly use it for tube circuit. I guess it was probably introduced around 1965-1966, I've checked the HP catalogs onhttp://www.hparchive.com/hp_catalogs.htm, and it doesn't seem to be mentioned before. It fully solid state, not tubes, and in fact, not a single IC for that matter, fully discrete ! In the middle of the 60s the tubes were being phased out, but there probably still was a market for that kind of device. It is capable of sourcing 100mA, which is more than enough to power a small single ended tube amp, a radio receiver (I guess), and probably vintage T&M instruments.At the time of its introduction, middle of the 60s, I guess this was a pretty advanced design. First, it is solid state and not tube! But it's rather its "architecture" with a thrystor (SCR) pre-regulator followed by a "classic" linear post-regulator, which make it very interesting. Even by today's standard, "two stages" regulators are not very common.Now for the teardown/repair.1) The unit is in pretty good shape, and the seller says it power up. The positive voltage connector is missing, the (ten-turn) voltage setting potentiometer and main filter cap (C14 filtering the output of SCR) were removed, but included in shipping. You can see at the picture that it is a metal can "Mallory" 125uF, 450V. By today's standard, it is huge and heavy. As one of its pin is broken, I wasn't able to test it . The ten-turn pot is broken (open).2) The first thing I've done is to rewire it for 220V operation (I live in France). Just need to break to traces on PCB (I used a drill) and solder a strap, see photo. This is well described in page 17 of the operating/service manual pdf.3) And indeed it powers up ! And basically, I was able to check the voltages of "reference regulator" and "bias supply" with both a DMM (voltage values) and scope (ripple, waveform), and they are ok. The unit has two transformers: One supplying the high voltage, and a smaller one for bias, reference, and for low voltage transistors. I guess both are ok, even if the HV xfrm measures a slightly less than expected voltage.4) As you can see on the photo of the "lower side", there's some signs of a "heat up". This is probably resistor R81, right after the SCR output but before the pass transistor.5) I've started to check the SCR regulator, especially the circuit in charge of fire it. Waveforms appear ok and I guess it is functional.6) Currently I've no idea of what is the problem of this unit. But the next step would be to solder a replacement filtering cap, a 100k potentiometer for voltage setting, and a connector.The operating/service manual is really great because it gives the complete theory of operation, along with a step by step debug/repair instructions.I have great confidence that I will be able to fix this unit completely. I'll keep you updated if you guys are interested.

author: anotherlin
author_rank: Frequent Contributor
timestamp: January 20, 2015, 01:50:10 pm
content: The photos of the harrison supply of my first post are gone. I repost some of them. As you can notice, the circuit didn't changed much between the older and newer revisions.

author: BeltAndBraces
author_rank: Newbie
timestamp: January 21, 2015, 12:07:24 am
content: I myself have another supply from the HP/Harrison time: the 6823A Power Supply - Amplifier. Both of them share one design aspect that I find really neat. They use the entire back of the device as the heatsink, part of which folds into the case and directly on top of the PCB. This way they can mount the TO-3 package on the heatsink and solder its pins directly to the PCB. Very clever!

author: AMR Labs
author_rank: Frequent Contributor
timestamp: March 27, 2025, 07:05:50 pm
content: Old thread but hoping someone might have the HP6209B service manual that includes the PCB and component layout? I've got the one that seems to be everywhere, PN 06209-90003 from June 1969, and it has the schematic but no board or component views. It is also meant for serial numbers starting with 7F1117 and above. Mine is SN 7F10xx so slightly bellow that breakpoint.The link to Keysight provided by the OP did not work for me, but would not be surprised that it was to the same version manual as that I already have.Mine seems to be working fine, output voltage range checks out, and voltmeter scales are reading fine now after calibration (they where about 5V high).Only issues are some rather unusually stiff and somewhat hard to turn (but working) current 10-turn pot, and also when I switch the meter to 12mA range the needle pegs all the way to the left beyond zero, even without any load connected. The 120mA range seems ok other than it was reading a bit low, but calibration solved that. If I put a 10mA load and select the 12mA range it reads around 8mA, even after the previous calibration of the 120mA range, and pegs again to the left after a second or so once the load is removed. Guessing an out of tolerance resistor in the current meter circuit, but it would be easier and more convenient to track it down if I had the parts location on the main board as some parts label designations are obscured by the part itself. Otherwise guess I'll just map out all the board components.TIA.

author: TimFox
author_rank: Super Contributor
timestamp: March 27, 2025, 07:35:36 pm
content: Responding to an old thread.I own two 6209Bs that are very useful for my vacuum-tube experiments: both were eBay purchases.The first one was in good condition; I tested the second with a power resistor load and hand-held DVM and it seemed to work.However, when connected to a grounded load, the output was very low.I found that a rubber grommet used to mount the PCB was actually in contact with one trace on the PCB.It had charred badly, making a connection from the PCB to chassis.I replaced that grommet with a plastic washer to fix the problem.The grommet was at the corner of the PCB closest to the left edge of the front panel (seen from the outside).

author: AMR Labs
author_rank: Frequent Contributor
timestamp: March 27, 2025, 08:23:01 pm
content: Noted, and thanks for the heads up.

author: AMR Labs
author_rank: Frequent Contributor
timestamp: April 01, 2025, 06:06:56 pm
content: Turns out C12 was bad. Its a 450uF 85V cap in the bias supply, and it measured 135nF. The +43V supply was only showing 34.2V, but when I set the DMM to AC there where 14VAC of ripple across the cap.After replacing the cap with 470uF 100V the voltage rail came up to +43.4V and the meter on 12mA scale no longer was pegging to the left, but now rather showing 4mA with no load. Had to adjust R38 and that brought it down to zero without affecting the general zero adjustment of the meter. Then went through the meter calibration routines for both voltage and current and all is good now.The other big caps, C14 and C20 both tested good so left them alone. Ripple at the output set to 320V with a 100mA load is about 1mV.