SCR-508 radio - BC-604 Transmitter - diagnosis tips?

Radio Telephone and Telegraph Transmitting and Receiving Equipment
Big D
G-Captain
G-Captain
Posts: 787
Joined: Sat Sep 19, 2009 11:22 pm
Location:

Re: SCR-508 radio - BC-604 Transmitter - diagnosis tips?

Post by Big D » Tue Jan 16, 2018 11:56 pm

Hi Radtech,

Very good. Thanks for that. It sounds like all is well then.

I have the tubes and microphone on the way so will provide another update in a few weeks to let you know how I got on.
Darryl Lennane
NZ

1943 Willys MB
1941 LP2A MG Carrier
1943 White M3A1 AOP
1942 Willys MBT
1944 Ford M8 Armoured Car
1945 Ford M20 Armoured Car


Big D
G-Captain
G-Captain
Posts: 787
Joined: Sat Sep 19, 2009 11:22 pm
Location:

Re: SCR-508 radio - BC-604 Transmitter - diagnosis tips?

Post by Big D » Mon Feb 05, 2018 11:00 pm

Hi all,

I got the parts I was waiting for and fitted them today.

I replaced the capacitors on the HV end of the DM-35 dynamotor in the BC-604 with two new ceramic capacitors. I think the change slightly improved the dynamotor whine while it is running. It is a little hard to know how much should be heard without having heard one before so I will reassess once I have everything installed in the vehicle.

I also replaced the two audio tubes with two known good tubes. I'm not sure that these made much if any difference in the audio quality, but at least I know now that these are working.

I also tested the set with a known good T-30 microphone. Again, no difference in the audio quality over the other microphone.

Out of interest, I tried using an SW-141 ( CD-318) chest rig and a T-17 throat microphone. The audio on this was noticeably crisper than with using the T-30 microphone.

As I say, a little hard to know what to expect without trying one before, but the latest test with this T-30 setup was encouraging.

While I was adjusting sidetone levels the dynamotor started running all the time again. You might recall that this seems to be an intermittent problem I'm having. I don't know whether it would be related to me adjusting the sidetone but I have a feeling the problem happened last time when I was doing this.

Radtech - I've had someone else say that the dynamotor should not run all the time in Interphone mode, and referred me to page 47 of TM 11-600. The bottom of page 40 of the TM-600 manual also seems to confirm this.

If that is the case, I still have a problem somewhere, but I think progress is being made!

Thanks.
Darryl Lennane
NZ

1943 Willys MB
1941 LP2A MG Carrier
1943 White M3A1 AOP
1942 Willys MBT
1944 Ford M8 Armoured Car
1945 Ford M20 Armoured Car

iowadeadeye
G-Sergeant
G-Sergeant
Posts: 48
Joined: Wed May 11, 2005 8:22 am
Location: Elk Horn, IA
Contact:

Re: SCR-508 radio - BC-604 Transmitter - diagnosis tips?

Post by iowadeadeye » Sat Oct 13, 2018 5:13 pm

Hi,

Have a SCR 508 system in my tank and trying to get the interphone systems working. First, what are the correct switch settings for this operation and Second, is there any changes for the wiring. I followed the wiring diagrams in the books. I have correct power and dyno’s fire up with lights on the xmtr, and receivers. Any suggestions for a first start up of the interphone system. Once I have this working, then I will work on the transmitter portion.
Son of a Deadeye (96th Infantry WWII)

Big D
G-Captain
G-Captain
Posts: 787
Joined: Sat Sep 19, 2009 11:22 pm
Location:

Re: SCR-508 radio - BC-604 Transmitter - diagnosis tips?

Post by Big D » Sat Oct 13, 2018 8:01 pm

Hi there,

It has been several months since I did my interphone setup so apologies if I am sounding a bit rusty on it. I’m sure I’ll remember more as we go. Here are a few ideas to get started based on my experiences.

The BC-604 and BC-603’s should be switched to Interphone. If you are running two BC-603’s, I’d be inclined to try one BC-603 first and leave the second one off. The Radio/Int switch on the BC-606’s should be switched to Int.

Plug a T-30 microphone into the BC-604. With the power turned on, when you key the T-30 microphone you should hear the dynamotor on the BC-604 start up. The dynamotors on the BC-603’s run all the time.

Can you hear any audio coming out of the speaker on the BC-603 when you key the microphone? If you can, then that is a good indicator that the FT-237 and the set(s) are wired correctly and working okay.

The next thing I’d try is to plug in an HS-30 or other headset into one of the BC-606’s and see if you have any audio. It made sense to me to get the audio working on the BC-606’s first before worrying about the voice.

Key the T-30 running off the BC-604 again and see if you can hear audio in the headset. If not, try plugging the headset into one of the other BC-606’s. If you can hear audio, move to trying a T-30 microphone in one of the BC-606’s and see if you hear audio in one of the other BC-606’s.

Dependent on the result, can you photograph the wiring on your BC-606’s and post them here please? Can you also scan or photograph the wiring diagrams you used and post them here. I don’t think there should be any differences between the wiring on your setup or mine, unless there is a difference to how the terminal on your FT-237 is configured.

Good luck and keep us posted. If I think of anything else in the meantime, I’ll let you know.
Darryl Lennane
NZ

1943 Willys MB
1941 LP2A MG Carrier
1943 White M3A1 AOP
1942 Willys MBT
1944 Ford M8 Armoured Car
1945 Ford M20 Armoured Car

User avatar
wa5cab
CWO4 (Ordnance) USNR
Posts: 2064
Joined: Sun Dec 29, 2002 11:22 am
Location: USA/TX/Houston
Contact:

Re: SCR-508 radio - BC-604 Transmitter - diagnosis tips?

Post by wa5cab » Sat Oct 13, 2018 10:31 pm

Couple of corrections - not counting the T-50 Dynamic mic and what the British used, there were three microphones commonly used with the SCR-508/528. The T-17-(*) is a hand-held single button carbon microphone in a cast aluminum or plastic housing that looks like a large lollypop and has a black button on the side for Push To Talk (PTT). The T-30-(*) is a two-button carbon throat mic and requires Cord CD-318 for PTT. It is easily the worst of the bunch for audio quality. The most common by far is the T-45 single button carbon lip mic which also requires a CD-318. It is the best of the three for audio quality but the Army version is a little uncomfortable to wear because of the elastic loops around the ears. It replaced the T-30 in service from about 1943.
Gunner
USN Retired
MVPA 9480

Big D
G-Captain
G-Captain
Posts: 787
Joined: Sat Sep 19, 2009 11:22 pm
Location:

Re: SCR-508 radio - BC-604 Transmitter - diagnosis tips?

Post by Big D » Sat Oct 13, 2018 10:38 pm

Hi Gunner

You are right. My mistake. The T-17 microphone was the one I was meaning for use for testing.

Interestingly, not sure whether I had bad luck with the two T-17 microphones I used but the NOS T-30s I tried had great audio quality and were much better than the T-17s. I found boxed ones were considerably better than others. Maybe the carbon element deteriorates? The only T-45 I tried didn't work at all!
Darryl Lennane
NZ

1943 Willys MB
1941 LP2A MG Carrier
1943 White M3A1 AOP
1942 Willys MBT
1944 Ford M8 Armoured Car
1945 Ford M20 Armoured Car

User avatar
wa5cab
CWO4 (Ordnance) USNR
Posts: 2064
Joined: Sun Dec 29, 2002 11:22 am
Location: USA/TX/Houston
Contact:

Re: SCR-508 radio - BC-604 Transmitter - diagnosis tips?

Post by wa5cab » Sun Oct 14, 2018 11:15 am

Yes, a lot of T-17's do have bad or at least stuck/clumped carbon elements. The same thing can happen to the T-30's and T-45's, and the same cure sometimes works, although it is easier to tap the T-17 against a softwood board than it is the other two. In normal use, the T-30 is strapped around ones neck, over the voice box. However, the audio available at that location is muffled and lacks the higher frequencies that are present in front of ones mouth. That's why they sound muffled. If you rig up a stand and use it like a desk mic, they sound OK but will have lower output.
Gunner
USN Retired
MVPA 9480


Post Reply

Return to “Radio's and Communications”

Who is online

Users browsing this forum: No registered users and 25 guests