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Rebuilding the Collins 30L-1

Created by James W Benedict, N8FVJ on 2021-10-30

 

Rebuilding the Collins 30L-1

 

The Collins 30L-1 is due for a rebuild. I read some Hams are still using the original build, but the HV capacitors are way overdue for replacement. The info below is not my suggested rebuild, but an accumulation from other experts. However, I will add some info from the Duncan PSUII power supply simulator.

 

First, the Collins 30l-1 has some stability issues on 15 & 10 meters with certain load and tune capacitor positions. This is documented by Don Jackson W5QN in the 2013 Q4 publication from the Collins Collector Association. Bottom line, change the 39uH inductor L3 with 72uH at 1 amp or larger and bypass with a 3.3K 1/2 watt resistor. All instability issues went away. Mouser part number is EPCOS #82111EC24.

 

New 811A tubes have been known to short from plate to grid. This can cause damage to the bias circuit and relay coil. Install a 200-to-250-volt MOV across C2. Any MOV of about 1/2" diameter can handle the inrush current.

 

The 100uF high voltage capacitors are long overdue for replacement. Axial capacitors are far too expensive. I use the snap-in type and solder a lead to connect the one end to the other terminal. 100uF is rather small in value and average 150 volts of AC ripple using SSB. Increase the capacitors to 220uF to reduce the AC ripple in half. I would recommend a capacitor of 1.5 amp ripple current. Nichicon LLG2W221MELA35 fits perfect with the high ripple current rating. Voltage doublers stresses the capacitors more than a bridge rectifier thus the high ripple current rating.

 

The old 600-volt diodes should be replaced. The peak current thru the rectifiers as shown on the power supply simulator using SSB is 4.5 amps. I have seen 1N4007 work but would recommend 1N5408 3 amp @ 1KV diodes. Collins used eight 600-volt diodes per leg, but you can use five 1N5408 per leg to get the same PIV rating as the Collins design.

 

As for replacement 811A tubes there is only one company called Psvane building the tubes. I know zero about them and no reviews of the tubes exists in eHam Reviews. some older stock tubes by Penta and Machlett are on eBay and the manufacture was Shuguang that is not in production. RF Parts at the moment has quads of 811A tubes in stock from Shuguang. RF Parts screens every tube for quality. I use the Russian G-811 that is the same as the older Svetlana 811A. I find these tubes advertised on eBay. I been using the G-811 at 600 watts SSB PEP out and have no visible red plate issues. In an eHam review, another ham has been using these G-811 tubes for 20 years without failure. There is one person who may reply the tubes have an undersized plate and junk. The plate is the same size as other 811A tubes from China and both China and Svetlana rate the G-811 tube at 60 watts ICAS plate dissipation. Perhaps only a 57-watt ICAS plate, all I know is I get 600 watts PEP out without any issue.

 

A more powerful tube to use in the Collins 30L-1 are the heavy duty 572B. Instead of a 5 second tune up time and 600-watt PEP output limit, the 572B can stand much longer tune up time and higher output as well, Collins rated the 30L-1 at 1KW input that at 60% efficiency is 600 watts out. I read some have produces upwards of 800 watts PEP out on the lower bands, but not recommended. It is a SSB amp, not an AM amp that are more heavy duty. Psvane is the only supplier in the world and as mentioned does not have a track record. RF Parts is out of stock, I believe HRO has stock at the moment of the older Shuguang 572B older 572B stock may still be for sale on eBay. A quad of the 572B are around $350.

 

If anyone else has some rebuilding tips, please add your comments. As stated, I am not an HF amplifier designer, just repeated info found on the internet and added some info from the Duncan PSUII power designer software simulator.

 

 

K6RMR2021-12-05
Rebuilding the Collins 30L-1
Only Use 811's that have a Reinforced Grids. Since the Tubes are run Horizontal The Grid will sag and it the Plate. The Original RCA's did not do this. I bought some tubes from Alpha Amp that are from China but the Tubes is Properly Build and have had not trouble in 4 years. Also the Plate Current has to be set Properly according to the Manual. I do not aloue my apy to draw more than 600MA. If you just tune for max output you will destroy the Amp.
N4TD2021-11-22
Rebuilding the Collins 30L-1
My friend W4NL asked me to make his 30L1 full break-in keying some years age. The modification worked very well and got rig of the high voltage on the TR jack. A small NPN transistor would key it without problem. I agree upgrading the 30L1 makes it a much more viable amplifier.
N8FVJ2021-10-30
Rebuilding the Collins 30L-1
BTW- the article just stated the Collins modifications. You have to replace the bias capacitor and best to replace the diode with a 1N4007 when performing a rebuild.