I am about to undertake an old Philco with Loktal tubes. Last night I decided to run the tubes past my tube tester. It is a Hickok 546. When I bought the tester the roll chart was missing. After many days of internet dredging, I decided that the chart for a TV/3 tester (not the a/U, B/U, or C/U.) should be very close as it used the same signal levels and had the high-low signal switch. The only difference appeared to be the use of a range switch for Gm instead of using the English pot preset points. I got a roll chart for a straight TV/3 off of ebay and I have been using it with some success. Until the Loktals. The radio has 6 or 7 of these beasts in it. Two of them came up with shorts (the rectifier and a 7C6). All of the others pegged the meter with Gm set for it's highest range (10,000 on this tester). If I crank up the bias to roughly 2 times the setting it comes down off of the peg but is still way too high.
The question is, is this a tester thing or something going on with the tubes? I am trying to decide whether the tester migh have a problem, the settings are no good, or the tubes have some problem. At first glance the tester settings seem reasonable to me based on the specs for the tubes. I can't imagine what kind of tester problem would make the gain look so high just for the Loktals. And I can't imagine a tube failure that would get past the shorts test and make the gain look high. Any ideas?
By the way, I removed the tuning cap from the Bremer and patiently massaged the plates to the point where they don't short out. Not as bad as I thought. The radio works but the selectivity is horrible. My AK48 is 10 times better. I am going to check for high resistance in the tuning cap.
http://www.keyboardpartner.de/tubeworks/hickok/hickok_bias.htm
The 7B8 bias setting for my tester is 18 which gives a bias of about 2.3 volts. The signal level is 5 volts. This doesn't seem right, does it? The 546 and the TV3/U have signal levels of 5 volts (normal) and 1 volt (low). The chart says to use the normal setting for all of the Loktal tubes that I tested.
Regarding sensitivity, leakage in the tuning condenser can be a problem, so you are going in the right direction. If a condenser has residue on it (cigarette smoke or other polution), it can be removed by washing in mineral spirits and then by giving it a hot soapy bath. Rinse with piping hot water and dry in a 170 degree F oven.
Intermediate frequency adjustments must also be critically adjusted for superb selectivity. Antenna trimmer adjustments must be made as well as possible. Some radios with oscillator padders and trimmers can be nightmarish. I'm not sure what your Bremer has for circuitry. I have a Philco 60 which has the oddest thing (they all are this way). It has no trimmer on the secondary of the 2nd IF. This ruins any hope for good selectivity. I modified the circuit by inserting a trimmer/choke series combination in series with the detector lead. I couldn't effectively place a trimmer across the secondary with any good results, so I went this way instead. It works wonders. Actually I forgot how I have the trimmer and choke wired. Either they're in series or in parallel. Can't remember.
Thomas