The TS-511S Continues


Here is another brochure showing the TS-511 and matching Power Supply and VFO.

Installing the "real" T4 was going to be easy, but first I wanted to see what the receiver sensitivity would be with my homemade transformer. I decided to measure the AGC voltage on Pin 1 of the 1st IF tube and the audio voltage at the speaker as I slowly increased the RF signal generators input to get a reading of S9 on the meter. I used my calibrated Wavetek model 3000 and a Kenwood VT165 AC voltmeter and a Keithly 175 multimeter in the test set-up described in the TS-510 manual. I set the volume control at 50% and plugged into the phone jack to get a signal into my AC voltmeter. Once I got my readings at a few different frequencies I repeated the test with the "real T4". You can see the results below in table 1.

Table 1

Signal Level HBCoil (dBm)
Signal Level Real Coil (dBm)
Freq MHz
S9 Voltage
3.7 MHz
7.2 MHz
14.2 MHz
21.2 MHz
28.2 MHz


Wow, the real coil makes almost 10 dB difference! Wonder how that will impact the transmitter?

The Transmitter

This Radio was designed to compete with the SWAN series of radios being offered at the time. The TS511S uses two sweep tubes like those used in Color Televisions of the day to produce an incredible amount of Peak Power. The finals, 6LQ6s are supplied with 900 Volts on the plates and can draw 400 to 500 ma on peaks although the average current is much less than that. Finding these tubes today is difficult and expensive. The two that were in my radio were both bad and needed to be replaced. I luckily had a NOS set of 6JE6 tubes that are a direct sub. I did not have a NOS driver tube however and so to begin my tune-up and adjustment of the transmitter section I used a weak driver tube. A new 6GK6 would need to be purchased. Originally the radio smoked a 100 ohm resistor that supplies DC to the driver. I found the original driver tube shorted and I replaced R7 a 100 Ohm resistor in the plate circuit.

When I started the work on the Transmitter section the first thing I did was check the DC supply voltages. I found the 150 volts and 300 volts to be right on with low AC ripple. However, the 900 volt DC supply was only providing about 680 volts. A quick check of the power supply showed that both of the 100 ufd / 500 volt capacitors in the voltage doubler circuit were leaking and had a high ESR. I changed these out and the High Voltage returned to 1000 volts no-load and about 900 volts under load.

Next I revisited the coil bank tuning procedure that I had done previously to align the receiver. Since these coil packs serve double duty in both the transmitter and receiver mixers and driver/RF amp circuits I didn't expect much to be done other than verifying the transmitters performance. Starting with 3.7 MHz the transmitter was placed in CW mode, the key jack shorted with a jumper lead, and the tune up followed. 80 meter yielding over 120 watts output. Next I went to 28.5 MHz, then 21.175 MHz then 14.2 MHz and finally 7.150 MHz as described in the manual. Everything worked fine until I got to 7.150. The 40 meter band was nearly dead with only 25 watts of output. I suspected the band switch or perhaps a capacitor failure in the driver tuned circuit.

I removed the driver band switch board and carefully removed the rotary switch. Using a magnifier I inspected the switch and all of the coils. Since I had the switch removed I dropped it in a glass jar full of TarnX. The black corrosion instantly dissolve revealing bright and shinny switch contacts. Finding nothing wrong with the mechanics, I check all of the band coils and the associated capacitors. Everything was fine. I reassembled the radio and retested the transmitter only to find 40 meters was still weak.

L6 had changed value from 100 to 50 uH and upset the tuning on all of the bands but it was most noticeable on the 40 meter band.

Well, to make a long story short. I ran a few more tests and determined the problem had to be in the driver coil bank. I had tested all of the parts on the board except one. The 100uH RF choke. Now I usually don't see these fail, but I did replace R7 when it burned up due to a shorted 6GK6. I now suspected that the coil that is in series with R7 had been damaged. I removed the coil and measure it. It measured a little over 50uH and once replaced 40 meters was working as well as the other bands. I would never have suspected this little RF choke to make such a difference or to impact the tuning. I retuned the coil banks again and noticed improved sensitivity and good transmit output on all bands.


Here is the little 100uH RF choke that caused all the trouble.

The clue was that both RX and TX circuits were showing lower gain than expected.

The Microphone amplifier in the TS511 is transistorized and is shown is the schematic at the left. Q1 is a general purpose FET and it is followed by a two transistor direct coupled amplifier.

In these old radios I always check the electrolytic caps with an ESR meter. C3, C4,C5, C10, C11 and C9 are the ones to check in this circuit. They are all audio coupling caps or bias bypass caps that if open can cause audio level problems.

The TS511 requires a High impedance microphone.