Collins 30L1 tuning

[W2DHB]

I acquired a 30L1 amp, with 572B tubes, in Feb from a SK. My transceiver(s) are Yaesu FT101B & F101ZD. Using a Bird 52 ohm dummy I loaded the rigs, with amp off, to 100 or 70 watts out in tune (swr 1.1). A). Turning on the amp, (118vac) I followed the manual for tuning, noting the 30L1 loading  was at "1" at max RF out into the dummy load (would only produce 200 watts, adjusting it lowered the RF out). HV = 1.8kv, current slightly over 200 ma under load. I noted the swr between the xcvr and amp was just under 3 with a bird wattmeter. B). I looked at the input tuning adjustment because the swr should be no more than 2. Although the manual said you could change the swr, I could not adjust it via its tuning slug. In testing, I only looked at 3.5 and at 28 mhz input tuning. I also tried a MFJ204B antenna bridge with the same result. Does this problem(s) sound familiar? Is it the: Tubes? Tuning? Other?

[WA1GFZ]

I wonder if an input coupling cap is bad??
Not sure if you can monitor grid current but maybe that would give a clue.
Sounds like drive isn't getting to the tubes or the tubes are shot.

[kb3ouk]

I have a similar amp, the Hunter 2000B (basically a copy of the 30L-1, even looks a little like one) that I use with an FT-901DM. My amp does not have a perfect SWR at the input when the amp is on. The reason you were seeing a low SWR when tuning the Yaesu into the amp was because you had the amp turned off. When the amp is off, the transmit/receive relays in the amp won't function, so your transceiver was feeding the power directly into the dummy load. What I do is tune the rig at full power into the dummy load, then tune the amp. Once I get both tuned up, I key the Yaesu while it is hooked to the amp, and tweak the Preselect, Plate, and Load controls for full output while feeding the amp. Since you are using a tube rig, that 3:1 SWR isn't anything that I would worry about, since the Pi-net in the Yaesu can be tuned to be matched to the load that it is seeing from the input of the amp. The other thing is that high SWR will only appear at the rig when the rig is transmitting. When receiving or operating with the amp turned off, the SWR at the rig's antenna terminal will be the same as the SWR at the antenna out on the amp, since the RF would be bypassing the tube circuitry in the amp.

[W2DHB]

Thanks for the replies. I know you can tune for maximum smoke and ignor the Collins manual on tuning. However, when doing so I still have only about a 3 db  gain (70 watts gives me about 150 watts in tune, and on 40 meters I get tvi (cable  tv). (my FT101B will give at least 125 watts in tune without the amp.) When I first got the amp (2/27/12) I could get 400 watts output at 300 ma with 70 watts drive from the FT101ZD in tune. I'll start looking for replacement 811s or 572Bs and take a look at the bias.

As far as the 30L1 broadband input tuning, My MFJ-204B antenna bridge  indicates the lowest reading (5) at 4.8 mhz at about 20 ohms with the 30L-1 in the 3.5 bandswitch pos and the ant relay keyed. With the MFJ set at 50 ohm at 4.8 mhz, the meter reads (20). Bird 52 ohm dummy load reads (0). What I don't understand is my inability to change the reading by tuning the input circuit (L18).

[Opcom]

I'm going to fish around.

L18 is the 3.4-5Mhz coil, you are testing at 4.8Mhz. Could L19 be open?

Can you disable the B+ and drive the amp with a harmless power level maybe 10 watts, and use a scope to look at the RF signal from the input jack to the 572B filaments, and see that it is getting there -to each one?

Could the coil L18 be already at its minimum inductance as might be possible at the upper end of the tuning range? L18 must affect the tuning unless maybe it is not receiving the RF.

Could C18 or CR18 be damaged or shorted? It is the ALC circuit but if it was bad, could short out some of the drive.

What happens on other bands?

I will say that 30+ years ago, before I had a license, I bought a Gonset? amp with four 811A's at a garage sale for $20. The tubes were so shot the amp would only make 100W when 100W was driven into it. I gave it to a ham, who checked it and verified the tubes were shot, and passed it on to someone who wanted to re-tube it for SSB use. Can you borrow a set of 811's locally for a try? Someone ought to have a few usable ones.

[W2DHB]

I appreciate the reply. I was adjusting L18 because it affects the 80 M band (band limit range from 3.4 to 6) trying to lower the impedance and where it resonates. I loaded the 30L-1 on 3.990 mhz and then checked the input with the antenna bridge. The bridge indicated about 4.8 mhz at the lowest dip and could be lowered further by adjusting the bridge resistance to 20 ohms.  I could not adjust L18 from outside the cage because the slotted slug was damaged, I had to power down the amp, take off the cover and adjust it from inside (a very slow process). However, L18 adjustments did not seem to improve the bridge (or SWR) reading on 3.990 mhz.  Another post elsewhere on the Internet, said bad tubes will affect the input swr. So it looks like I may need new tubes. Assuming the the meter is accurate, I will have to get 572Bs because the HV is 2 KV (1.8 KV under load at 200 ma) and the 811A has a 1.6 KV limit.

Thanks for your suggestions, I keep working on my problem for answers and see about getting or borrowing some new tubes.

[KM1H]

Chinese 811A's will self destruct in that amp and even JAN 811A's are seriously stressed.

Understand the position of the Loading control in relation to the position of the variable cap. You ALWAYS want to start with low C so as to not exceed grid current.

NEVER start with the Tuning at 1 as stated in the manual, that is almost full C and is one of the quickest way to destroy the tubes.

This is especially critical on 10-15M where the tuning can be a bit squirrely especially if the parasitic suppressor resistors have been cooked and gone up in value.

If it is a ROUND emblem version it has all the factory changes, if not get them from the www.collins.org site.

There are also many other mods out there, some good and a few downright stupid. If in doubt ask.

Check the 4 grid resistors as they are prone to go way up in value or open up so you may not even be driving all 4 tubes.

I happen to have a 30L1 in for service and updates (its an early winged model)so can likely work along with you if you get bogged down.

If not already done the PS board should be rebuilt as those caps are long past safe service life. W6BN was selling an excellent replacement board, all complete but he went SK last May. Harbach has a nice kit version available.
http://www.harbachelectronics.com/main/page_products_collins_equipment.html

Carl

[W2DHB]

Carl, Thanks for the reply.

According to my Collins manual, you should start the loading at "1", which is fully ccw (full mesh). Perhaps it was a typo and you were to start at "10". However, I started tuning up at midway, and usually ended up at "1" at maximum power. I checked the amp against the schematic and service bulletins and it has all the changes I found. By the way, your link to Collins is not correct (it is a personal site with family pictures).

In my inspection, I found the HV caps and rectifiers had been changed; the grid resisters were 47 ohms and all within tol.; and the bias was -266.7 V on key up, and -2.89 V on key down. My next step will be to swap tubes with a friend and compare tube performance.

Pat

[W2VW]

Don't bother with any 811s if planning on using AM. None will live in that amplifier.

I used some of the Asian 572B's available a couple years ago and got a year out of them with 125 watts carrier out before selling the amplifier. No decrease in performance from day one was noted.

I had to remove one screw from one tube socket to clear the tube base keyway during installation. The screw can be re-installed after plugging the tube in.

[KM1H]

I forgot a word and meant this

http://www.collinsradio.org/archives/Collins_Radio_Equipment_Manuals.aspx

or

http://www.collinsradio.org/html/manuals.html

Thats not the only manual that got loading control numbers mixed up since its ass backwards from what sounds logical. Anyone who has spent time with S line manuals realizes they hired the indigent to be proof readers.

Your readings look good.

[kb3ouk]

That's what gets confusing at times because isn't it when increasing the amount of loading you are decreasing how much the cap meshes? Some amps are labeled so that 1 is the heaviest loaded and 10 is the lightest.

[KM1H]

Thats correct in most amps and is what really confuses many since the Tune cap numbers make sense with the amount of mesh.

[W2DHB]

Thanks for all the suggestions and comments.
Found a buddy that ran 811As in his Heath amp., took my 572Bs over to try in his amp. that was running 400 watts with two tubes. Both pairs of my 572Bs would only do 170 to 200 watts when tuned up. Before doing any more work on my amp., I'll have to get replacment tubes,  Thanks again, Pat W2DHB

[w5gw]

The 30L1 is capable of 1,000 Watts input power and will produce between 600-700 PEP output power with 811A tubes.  I'd suggest using good quality 811As versus 572Bs just because they are cheaper.

Don't use the tune method in the manual (the tune for zero circuit is usually off - unless this circuit has been kept aligned it will give false results). 

Instead, apply 20 Watts from the exciter and tune the final and load controls for max output (should be on the order of 200 Watts) into a 50 Ohm load.  Don't try to load into a SWR of greater than 2:1.

If you run AM thru the 30L1 apply no more than 15 Watts of carrier.  That will result in 600 W output on voice peaks assuming a perfectly 100% modulated input AM signal.

Use a scope to monitor ouput wave forms on both AM or SSB.  It is easy to overdrive the 30L1 with a 100 Watt exciter.   

[W2DHB]

Thanks for the information, I'll correct my statement in my last posting. My friends amp was running 572Bs and about 2.2 KV. I was thinking about ordering my 811As from RF Parts, they suggest Taylor Tubes. I also found JAN 811A from a surplus place for about the same price for a matched set of 4. 572Bs will cost me twice as much, but I am concerned about the indicated 2000 volts on my 30L1 meter. Any reccommendations for supplier?

[KM1H]

Id stay way from surplus "matched" tubes as the only matching they likely have is all one brand. Plus many are at the point of having a bit of air leakage.

A 2000V stand-off voltage is OK for the 811A as they see more than that operational in Class AM use peaks.

OTOH the 572B can take more tuning abuse. RFP has 3 brands, all are OK as are the Ebay dealers. All come from the same factory, only the name changes.

Carl

[W2DHB]

  Thanks for all the help with this amp, the majority of my trouble with the tuning was with bad 572Bs. A matched set of 811As from RFP arrived and after a "burn-in" period, I tuned it up with 20 watts input and had about 100 watts max out into a Bird dummy load. The loading cap was about midway and my amp. input SWR was very low (1.1:1). Advancing to 70 watts input gave me about 400 W. output on tune. 73 to all that made suggestions, Pat W2DHB.