Author Topic: T-368/URT Transmitter Resource Page  (Read 389 times)

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Offline W1RC

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T-368/URT Transmitter Resource Page
« on: June 29, 2017, 09:01:41 AM »
I would like to compile a "spotter's guide" to the T-368 and its variants.

The manual set I have indicates there are the following

T-358/URT
T-368A/URT
T-368B/URT
T-368C/URT

In addition there are the following variants:
T-368D/URT
T-368E/URT
T-368F/URT (I have never seen this variant documented except my T3's id tag says it is an F model.........

The manual set consists of:

Instruction book for Radio Transmitter T-368/URT.  The manual written my the manufacturer which was delivered with the first batch and used as a basis for drafting the official TM11 manuals.  (in my library)
TM11-809 April 1955 The original "all-in-one" manual.  .pdf in the BAMA archives.
TM11-809-10 May 1958 Operators Manual (in my library)
TM11-809-20 July 1958 (.pdf in the BAMA archives.)
TM11-809-25 December 1958 Field and Depot Maintenance (in my library)
(Supplement C2 dated 6 December 1960 has schematics for the D and E variants)

You can download the manuals in the BAMA archives here:

http://bama.edebris.com/manuals/military/t368/

But the main point of this discussion is: How do you identify the variants especially the Modulator and Power Supply decks?  Only the RF deck has a metal tag and as delivered the transmitters were most likely all the same variant.  However in the world of depot repair, as witnessed with the R-390 and R-390A, the modules were interchangeable and many of the radios have mixed modules made by various manufacturers.  However each of the modules have an indication. Of the contractor who made them and a contract number. 

It might be an interesting exercise to see if together we can compile a definitive guide to the six variants of the T-368 by,chronicling the differences between the different variants.

Also if this has not already been done, let's see if we can compile a list of the different contractors, contract numbers and dates they were made.

My RF deck is a T368F serial number 106 made by TRW, Inc in Camden NJ Order number  14527(E)

Ross' is a T368C.  His is serial number 581, made by Crosley Div Avco Mfg Order No. 21316-PH-56

Here are a couple of excellent information pages on the T-368:

http://www.radioblvd.com/T368.htm

Bruce, W1UJR, had a great web page on the T-368 but it seems to have vanished into,thin air.  Wonder what happened to all that great material?  Here it is on the Wayback Machine archive site.....

https://web.archive.org/web/20070213154349/http://www.w1ujr.net:80/t368.htm

WA1HLR Audio Mods on the venerable AMWINDOW Web page......

http://www.amwindow.org/tech/htm/t368.htm

N9FOY Audio Mods

http://www.amwindow.org/tech/htm/n9foy/n9foymods.htm

73,

MrMike, W1RC


Offline W1RC

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Re: T-368/URT Transmitter Timtron Mods
« Reply #1 on: June 29, 2017, 09:06:33 AM »
Here are da Tron's Mods with the wallpaper......

So anyway, what ya need to do......

Speech Amplifier Modifications (Image file 1 at bottom)

The 12AT7 (V12) is now a cascaded amplifier. Notice the microphonium connector is floating from the front panel. The ground side of the jack is bypassed to ground with a 0.1 uF, 5 VDC disc ceramic cap. This is done to avoid ground loops that will occur between the modulator mainframe and the speech amp. It is useful to have a microphone input for a „just plug it in and playš capability. The usual D-104 or other high impedance type crystal or ceramic microphone offers a good compromise between broadcast quality and good talk power with the component values used.

There is no gain control pot used between the first and second stages. If the gain is too high and overload occurs, a 12AU7 may substituted for the 12AT7 or pot could be incorporated into the circuit. An additional BNC connector is used for a microphonium level input. This offers the use of a coax cable to the front panel and a good positive electrical connection to the input circuit. An RCA type connector may be used if this is the route you choose to go.

The audio bandpass filters and clipper stage (V14) have been removed. In earlier experiments, the 6C4 driver stage was tested with a larger cathode bypass cap (C21) and a larger negative feedback coupling cap (C40 changed from 2700 pF to 0.001 uF). This gave good low end response to about 80 Hz. Then the low end response rolled off as evidenced by a decrease in modulator plate current.

It was noticed, when a frequency response curve was performed using 400 Hz as a reference point, that the response at 3 kHz was down 5 to 6 dB! As the audio frequency was increased, the high end would continue to drop markedly while the modulator tubes continued to pull more and more current, until about 12 kHz. (This is a sign that the frequency response of the modulation transformer is okay but there is excessive amount of shunt capacity somewhere in the circuit, Ed.,HUZ). The problem is in the RF deck. We will get to that later.

The 6C4 driver stage was changed to a triode connected 6AQ5 (low mu) and the driver transformer was shunt fed. (This is also an excellent mod for Viking I‚s and II‚s, Ed., HUZ). A 5k, 25 watt plate load resistor and a 4 uF oil filled cap were installed under the chassis.

Notice that there is a 2 watt resistor across the secondary of T6, the driver transformer. In any situation where the tube being driven are operated predominately on Class AB1, it is very important to terminate the secondary of the driver transformer with a resistor close to its design impedance. This termination helps to reduce distortion caused by the transition from AB1 to AB2 (grid current on voice peaks). A type of clipping distortion can result. (The effect is noticeable on many stock T-368s when the modulation exceeds about 90 percent, Ed., HUZ). Also, the load resistor serves to flatten out the frequency response and rolls off the extreme highs. This latter is important when using negative feedback. If enough phase shift occurs is very high frequencies, ultrasonic oscillation will occur. (The effect on the life of the modulator is left as an exercise for the reader, Ed., HUZ).

With the new driver stage, the low end response appeared to go down to 30 Hz. Not bad for military iron!

Now, back to the beginning again. We have dual inpoots, 1) microphonium level, as previously described, and 2) line level. A 600 Ohm to grid transformer is used for dealing with balanced lines and good RF isolation. However, a typical medium impedance line level output, like that from your usual semi-pro and home entertainment equipment, can be used by going directly to a 25 k line inpoot pot. The two gain control pots (mic and line) are isolated from one another by a 47 k resistor. This makes the gain setting of each independent from the other.

Higher B+ was needed for proper operation of the speech amp. R12, a 10k wirewound resistor that is in series from the low voltage B+ to the audio section, has been jumpered out. Higher value dropping resistors are used for decoupling the speech amp. Further, a 40 - 80 uF electrolytic and a 470 Ohm resistor are used for decoupling.

Negative feedback is now introduced around the entire modulator in the form of five 1 MegOhm, 2 watt resistors from one of the modulator plates (right tube when view from the rear of the transmitter).

RF Deck Mods   (Image file 2 at bottom)

It is imperative that these mods are performed or else the high end response will always suffer. In the stock unit, there is about 6000 pF of capacity to ground, not to mention the two vacuum variable for tuning and loading. The circuit was converted to shunt fed by installing a single layer type RF choke, a B&W 800. A National R175 will also work, but may compromise performance on 160 meters due to lack of inductance.

The plate blocking and bypass caps used were 500 pF, 5kV CRL type 858 transmitting doorknobs. The end of L3 (1 mH) formerly connected to the B+ is now grounded. This puts the plate tank components at ground potential. The original blocking capacitors (C41, C42, C7) were left in place. It is a pain to remove them. C10, a 200 pF mica (bypass) was removed.

In the T-368 I worked on, there was an additional pie-wound RF choke in series with the plate current meter (M3). It was a convenient point to tie a length of high voltage wire and connect to the final tube where the other components are mounted (RF choke and 2 caps).

By removing the DC from the tank circuit, a possible source or arcing is eliminated. Further, the total shunt capacity is now about 1000 pF compared to 6000 pF in the original circuit. (This improved to the frequency audio response drastically, Ed., HUZ).

Final Thoughts

These changes allowed greater plate-to-plate swing of the modulator and therefore better us of the impedance match of the stock mod transformer. The transmitter at this point will do a bit better than 100% modulation in the positive direction. An improvement can be made by substituting 4-250s or 4-400s for the stock 4-125 modulators. The stock filament transformer will weather the storm but it will run HOT. A larger transformer should ultimately be used.

Air MUST be put on the tubes. A 4 inch muffin fan can be JS mounted to blow air between the tubes. Better yet, metal work can be installed to enclose the bottom portion of the chassis that contains the modulator tubes, thus pressurizing that portion of the chassis and blowing air from the bottom of the socket and over the tubes.

With the stock iron, there was a noticeable improvement in the low end response. Further improvement can only be obtained by installing a different modulation transformer. Space is limited. However, there is one type that appears to be made to order, the famous RCA 5500-to 5500 Ohm (1:1 ratio) open frame broadcast type. There is JUST enough space to install it. However, two electrolytic caps (C17, C18) that were part of the carbonium microphonuim voltage circuit must be removed. R19 is also jumpered out of the circuit. The new mod transformer will drop right on the chassis like it was meant to be.

Now 4-250‚s or 4-400‚s are a must. The DC current rating of the RCA transformer is 200 mA. Load the PA to only 200mA. DO NOT load the PA to the book value. The power outpoot is a little low but no one will notice. The transmitter will now easily modulate 150% positive. Al screen VR tubes are used (600 volts). The RCA iron has good, clean low end response and the high end response is as good as the stock iron.

There are possibly better alternatives for the speech amp mod shown here, but the main limiting factor is the mod iron. There is no room for anything larger. Also, 3-500Zs could be used for modulators with the proper audio driver circuitry installed...............

 

Offline W1RC

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Re: T-368/URT Transmitter Resource Page
« Reply #2 on: June 29, 2017, 10:20:06 AM »
T-368 Owner's Registry v1.0 (as of 16 August 2017)

There are currently 103 T-368(*)/URT transmitters (all variants) in the Registry. They are listed in model variant and serial number order starting with the earliest model and lowest serial number.  Contract or Order number is also requested.  Last known owner, when known, is indicated.  However, but much of this information is woefully out of date and comes from the former Registry that was compiled around 2001-2012.  Notwithstanding, for the purposes of the Registry, we are primarily interested in the transmitter, its' model/variant, serial number and the Contract/Order number and not so much as to who is its' present custodian.

You may send additions, deletions and corrections to list maintainer at t368registry@gmail.com.  Please do not repost the Registry to other sites.  Feel free to post the link.  The latest version will be posted at

http://forum.near-fest.com/index.php?topic=1350.msg3133#msg3133

For more information please see the T-368/BC-610 Yahoo e-mail reflector and message archives at:

https://groups.yahoo.com/neo/groups/T-368_BC-610/info

There is a BC-610 Registry from 2011 on the same site.  https://groups.yahoo.com/neo/groups/T-368_BC-610/database/2/edit

Thanks.

73,

MrMike, W1RC

July 7 2011 Registry: 
https://groups.yahoo.com/neo/groups/T-368_BC-610/database/1/edit

T-368*/URT OWNER REGISTRY AND SURVEY    v1.0   
Effective Date: 16 August 2017.

TOTAL T-368TRANSMITTERS ALL VARIANTS:    103

T-368   (Basic)       11       (1953-54)

W3TOY
Barker & Williamson #13
contract/order no. 3472-Phila-52

WB6DXR
Barker & Williamson T-368 #18
contract/order no. 25633-Phila-53

W9AMR
Barker & Williamson T-368 #22
contract/order no. 3472-PHILA-53
overhauled at Pirmasens Army Depot

WA1QHQ
Barker & Williamson T-368 #32
contract/order no.  25070-PHILA-54

NC4CB
Barker & Williamson T-368 #42
contract/order no. 14527(E)

KC8CU
Barker & Williamson T-368 #82
contract/order no. 21316PH-56
Overhauled at Lexington Blue Grass Army Depot

WA7YBS
unknown T-368 #104
contract/order no. unknown

W7QHO
Barker & Williamson T-368 #129
contract/order no.  25633-PHILA-53

K3PID
Barker & Williamson T-368 # unknown
contract/order no.  25633-PHILA-53

W2HU
unknown T-368 #138
contract/order no. unknown

W0WG (former call K0MAZ)
T-368
Exact details unknown.

Note: The two "unknown" contractors are most likely B&W.

T-368A         4     (1954)

KW1I
AMF T-368A #62
contract/order no.  25209-PHILA-54

KF2JQ
AMF  T-368A  #69
contract/order no.  25209-PHILA-54

AA9JC
American Machine & Foundry Co, T-368A #74
contract/ order no. 25209-PHILA-54

WB2FCN
T-368A
Exact details unknown

T-368B         1

AB3HT
Barker & Williamson T-368B # 9
contract/order no. unknown

T-368C       28.    (1955-1956)

WC4D (forme owner K4KWM)
Barker & Williamson T-368C #10
contract/order no.  43056-P-56

KA3OTT
Barker & Williamson T-368C #018
contract/order no. 43056-P-56

AE4IN
Daystrom T-368C #46
contract/order no.  28597-Phil-55

W5KP
Crosley T-368C #51
contract/order no.  28459-PH-55

K1KHP
Barker & Williamson T-368C #123
contract/order no.  43056-P-56

W9AMR
Barker & Williamson T-368C #152
contract/order no.  43056-P-56

NF6X
Barker & Williamson T-368C # 171
contract/order no.  No. 43056-P-56

W8KXR
Bendix T-368C #209
contract/order no.  3219-PP-59

W3PWW
Crosley T-368C #211
contract/order no.  28459-PH-55

W8KXR
Barker & Williamson T-368C #216
contract/order no.  43056-P-55

W7QHO
Crosley T-368C #237
contract/order no.  28459-PH-55

N4KIA
Crosley T-368C #275
contract/order no.  28459-PH-55

WB6ACU
Barker & Williamson T-368C #285
contract/order no.  43056-P-56
overhauled at Pirmasens Army Depot

AA9IL ( formerly owned by K0WRX)
Barker & Williamson T-368C #305
contract/order no.  43056-P-56

WA4VAG
Crosley T-368C #353
contract/order no. 28459-PH-55

W4TDC
Crosley T-368C #364
contract/order no.  28459-PH-55

WA0TSY
Barker & Williamson T-368C #367
contract/order no.  43056-P-56

W2ZR
Crosley T-368C #391
contract/order no.  28459-PH-55
overhauled at Pirmasens Army Depot

AA9JC
Crosley T-368C #530
contract/ order no. 28459-PM-55

WA0SPM
Crosley div Avco Mfg Corp T-368C #429
contract/order no. 28459-PH-55

KX4R
Crosley T-368C #560
contract/order no.  21316-PH-56

WB3ETN (from Fair Radio Sales)
Crosley Div Avco T-368C #580
contract/order no. 2131-PH-56
*FOR SALE*

W1EKG (former owner W1RC)
Crosley Div Avco T-368C #581
contract/order no. 2131-PH-56
overhauled at Pirmasens Army Depot

W9FM
Crosley T-368C #608
contract/order no. 21316-PH-56

WA3JS (Former owner AB3L)
Crosley T-368C #882
contract/order no. 21316PH-56

N2BC
T-368C # unknown
contract/order no.

WA4ZTY
Crosley T-368C # unknown
contract/order no. 28459-PH-55

K8OF
T-368C
Exact details,unknown

T-368D        6     (1958)

W4CT
Stromberg-Carlson T-368D #16
contract/order no.  no. 39692-PP-58

KE7KK
Stromberg-Carlson T-368D #33
contract/order no.  no. 39692-PP-58

K9RJ (SK)
Stromberg-Carlson T-368D #55
contract/order no. 39692-PP-58

KK1K
Stromberg-Carlson T-368D #57
contract/order no.  39692-PP-58

KA1KAQ (former owner W1DEC)
Stromberg-Carlson T-368D #104
contract/order no.  39692-PP-58

W4WSZ
Stromberg-Carlson T-368D #161
contract/order no.  no. 39692-PP-58

T-368E        25     (1959-1962)

W9XRT
Bendix T-368E #17
contract/order no.  3219-PP-59

KD1YT
Barker & Williamson T-368E #27
contract/order no.  15117-PP-62
overhauled at Pirmasens Army Depot

Scott (no call)
Bendix T-368E #102
contract/order no.  3219-PP-59

K4BVQ
Bendix T-368E #118
contract/order no.  3219-PP-59
overhauled at Pirmasens Army Depot

K6OSM
Bendix T-368E #133
contract/order no.  3219-PP-59

NZ1AF (former owner K4MK from Fair Radio)
Bendix T-368E #136
3219-PP-59
contract/order no.  3219-PP-59
overhauled at Pirmasens Army Depot

W2HER
Bendix T-368E #152
contract/order no.  3219-PP-59

KG2CI
Bendix T-368 E #160
contract/order no.  3219-PP-59

W3TOY
Barker & Williamson T-368E #206
contract/order no. 15117-PP-62

K7IOU (former owner W0ZR)
Bendix T-368E #224
contract/order no.  3219-PP-59
for sale $1995 7/2017

W9RAN (former owner KK4DF)
Bendix T-368E #238
contract/order no.  3219-PP-59
Overhauled at Pirmasens Army Depot

WB3ETN
Barker & Williamson T-368E #242
contract/order no. 15117-PP-62

K3IBX
Bendix T-368E #245
contract/order no. 3219-PP-59

W6TOM
Bendix T-368E #249
contract/order no.  3219-PP-59

W3GMS
Bendix T-368E #313
contract/order no. r 3219-PP-59

KF0HR
Bendix T-268E #353
contract/order no. 3219-PP-59
Overhauled at Pirmasens Army Depot

WB3ETN
Barker & Williamson T-368E #434
contract/order no. 15117-PP-62

K1KHP
Barker & Williamson T-368E #536
contract/order no.  15117-PP-62

KD3FA
Barker & Williamson 5-368E #541
contract/order no. 11517-PP-62

W3NP
Barker & Williamson T-368E #575
contract/order no.  15117-PP-62

K0BS
Barker & Williamson T-268E #577
contract/order no. 15117-PP-62

W7GVJ
Barker & Williamson T-368E #584
contract/order no. 15117-PP-62

KW4HF (former owner K4OZY)
Barker & Williamson T-368E #592
contract/ order no. 15117-PP-62

WF2U
Barker & Williamson T-368E #628
contract/order no.  15117-PP-62

K3FEF
Barker & Williamson T-368E # unknown
contract/order no. 15117 PP-62 MRF# 05690

T-368F         28         (1963-1967)

WA6IUR
TRW T-368F #2
contract/order no. 14527(E)

W5BVB
Oneida T-368F #19
contract/order no.  15498-PP-63

KK4XO (formerly owned by K1HH)
TRW T-368F #40
Contract/order no. unknown

WA1QHQ
Oneida T-368F # 59
contract/order no. 15498-PP-63

W1ZD
TRW T-268F #64
contract/order no.  14527(E)

W4CLM
Oneida T-368F #75
contract/order no.  15498-PP-63

Tom Leiper (no call)
ECCO Electronic Components T-368F #76
contract/order no.  DAAB05-67-C0022

W2ILA
ECCO Electronic Components T-368F #103
contract/order no.  DAAB05-67-C0022

W1RC
TRW T-368F #106
contract/order no.   14527(E)

W3RC
ECCO Electronic Components  T-368F #114
contract/order no.  DAAB05-67-C0022

KB1MCV (former owner W1JZ)
ECCO Electronic Components T-368F #115
contract/ order no. DAAB-05-C0022

KC9VF
Oneida T-368F #140
contract/order no.  15498-PP-63

W9QM
Oneida T-368F #149
contract/order no. 15498-PP-6

KA4JVY
Oneida T-368F #152
contract/order no. 15498-PP-63

USS New Jersey
TRW T-368F # 172
contract/order no.  14527(E)

K4OZY (former owner K4ATP)
TRW T-368F #184
contract/order no.  14527(E)

KF4TP
TRW T-368F #190
contract/order no.  14527(E)

WB3FAU
Oneida T-368F #192
contract/order no.  15498-PP-63

K9XH
TRW T-368F #238
contract/order no.  14527(E)
overhauled at Pirmasens Army Depot

N8FRP
Oneida T-368F #249
contract/order no.  15498-PP-63

NI6S
TRW T-368F #260
contract/order no.  14527(E)

N4FS
TRW T-368F #261
contract/order no.  14527(E)

KC9IEQ
TRW T-368F #262
contract/order no.  14527(E)

K2AUS
TRW T-368F #303
contract/order no. 14527(E)

W4ZF (former owner WA4KCY)
TRW T-368F #358
contract/order no.  14527(E)

W7XH
TRW T-368F #359
contract/order no.  14527(E)

W0VMC
TRW T-368FE # unknown
contract/order Jon  14527 (E)

W1UJR
T-368F

Variant unknown 0

CONTRACTORS       9

Contractor.                         Basic    A     B     C     D     E     F
Barker & Williamson              X              X     X            X
AMF                                              X
Crosley (Div AVCO)                                      X
Daystrom                                                            X
Bendix                                                        X             X
Stromberg-Carlson                                               X
TRW                                                                                X
Oneida                                                                             X
Ecco Electronics  Components                                            X

Known T-368(*)/URT Transmitters by Model/Variant

Basic         11
A                4
B                1
C              28
D                6
E              25
F              28

The T-368(*)/URT Owners Registry repository is courtesy of the New England Amateur Radio Festival, Inc, aka NEAR-Fest
Visit our site: www.near-fest.inc

Copyright 2017 W1RC