marconi: R8 & R9 values and others tips found on schematics
I am currently working on the restoration of a G.E. Marconi model 633W15 Type 296, and I found some differences with the schematics that is in the model information in RadioMuseum.
As you can see in the diagram, the values of R8 and R9 are not printed, and I could not find any reference on the Internet to know the original values. But what can be known in the diagram are the values of V-voltages across radio, so by doing tests I have come to the conclusion that the appropriate values for both R8 and R9 are: 68K Ohms. At least with those values I have achieved the correct values for V.
Another difference I have found is: in schematics CV4 appears inside IF1 and CV6 inside IF2, but when looking inside IF1 and IF2 there is physically neither CV4 nor CV6, therefore the primary of the IF transformers can not be adjusted. I think that both CV4 and CV6 were not factory installed because I seems that I am the first one opening the IF cans.
Another difference found in the schematics is that the denomination of the adjustable capacitor that is located in parallel with the D contacts of the bands switch is not printed: this adjustable capacitor must be labeled C5. This C5 is only active in LW-GO-OL.
Other difference found is that in the schematics a connection is missing: the upper contact of D switch must be connected to the junction point between L7 and L8. It has been physically verified on the radio that this connection exists but it is not marked in schematics.
I hope this information is useful.
Vicente Moncholi - Seville - Spain
Thank you very much for this information.
An identical schematic as shown here was uploaded to model Marconi Six (first series). Both files do not have original model or chassis information, this was added later. Furthermore, the schematic present here had "Typ 296" added to it while the model is a type 295. I have deactivated both as they were modified and are not strictly pertaining to those models - you can still find the complete schematic from the Schmémathèque Toute la Radio with notes at model Pathé 64.
As you can also read in the model remarks on both models, there are differences between chassis versions that we do not (yet) know. Currently the known chassis 633W, 633W1 and 633W15 are grouped together for simplicity.
Perhaps you can upload an image of the type plate for clarification. You write "633W15 Type 296" while we list this model as type 295. Unfortunately, the images present here don't have a sufficient resolution to read the plate.
Thanks and kind regards
I have submitted changes to the model to change the type from 295 to 296. This information was introdcued by me in 2016 based on the model name ("Marconi Six") and the available data at the time.
Also I have rephrased the model text to clarify that the "equivalent" Pathé model can be slightly different. We currently have no information if type 296 was delivered with chassis 633W, W1 or W15 - I am assuming that it's probably starting from 633W15 as this is a newer version than the original 633W.
We can only collect the data and come to a conclusion later on when sufficient evidence is present, or when we get hold of an original service manual.
thanks for your inputs.
I´m trying to do my best with this radio, correcting issues and verifying changes on schematics.
It seems I received a set complete with all original components, but in very poor condition: dust from decades inside, components degraded out fo tolerance,...
Has been very painful to put radio set to work because it needed to reconstruct almost all, including lot of cabling, the two capacitor blocks, dc filter capacitors, substitued all resistors except two, and all capacitors, and the type 47 tube.
Fortunately inductances and IF cans are OK, except discrete components inside, speaker and excitation inductance are OK, AF transformers OK, Westector OK.
By the way, I tried to susbstitute Westector with a pair of 1N54A and it worked, and then returned Westector on place to maintain it inside.
Here I attach photo of model and type.
When finish all test I download a corrected schematics as verified phisically on radio.
Thanks and regards,
- Marconi 633-model and type (293 KB)
Hope this info can help.
I have investigated the wiring of the speaker area to clarify the connection scheme from the radio chassis to the terminal strips plate.
Also to know the arrangement of the inductances: moving coil, excitation coil, auxiliary coils.
The diagram developed by hand is attached to help those who have to work with this radio.
Vicente Moncholi-Sevilla - SpainAttachments:
- Speaker zone wiring diagram (187 KB)
radio set now working OK.
Please find attached final schematics based on radio Pathé 64, updated as wiring and components found and verified on the radio Marconi Six model 633W15 Type 296.
Hope this may help others working on this radio.
Vicente Moncholi - Sevilla - SpainAttachments:
Hello Vicente and other contributors to this discussion and thank you for such detailed information that has helped me to complete the restoration of a Marconi 633W Type 296 this year.
Before I began to read the contributions here, with the help of the UK Vintage Radio Repair and Restoration Forum, I was able to identify the errors in the schematic that you have found here. I tried to attach the schematic that I used for my radio with the errors marked in red circles. Unfortunately it was rejected because it was larger than 300kBytes which seems very small to me. If anyone can give me some advice on uploading the schematic and some photos of the radio I would be grateful
Thank you Vicente for identifying the wrong component value for C2. Unfortunately I installed a 100pF capacitor in one of the boxes and had to remove it later on! I should have looked more carefully at the size of the capacitors I extracted from the box.
The problems I had in restoring the set were mainly due to very dirty wave-change contacts. They were so bad that the RF amplifier/oscillator section was not working on medium wave. After cleaning the contacts the radio worked well after a couple of attempts at aligning it. I replaced all of the bypass capacitors and 7 resistors, most of which had gone "high" and a wire wound resistor that had failed. The N° 24 oscillator/mixer was found to be faulty and was replaced. The N° 80 rectifier was noisy and that was fixed by soldering a loose wire on one of its pins. The HT filter capacitors were replaced with can capacitors from Germany.
I replaced the old bypass capacitors inside the two boxes by the following method:
1)I Put the boxes in the freezer overnight
2) The next day I used a block of wood to hit the boxes and shatter the resin that was around the capacitors. All of the capacitors fell out.
3) Using a tag strip I soldered replacement capacitors to it and inserted the tag strip into each box.
I have tried to compress images for this discussion but I have only had success with the schematic with corrections which I have uploaded here.
I have a Macbook Pro and am using an application called "Imageoptimiser". I used "Imageoptimiser" to compress one of the photos to about 740kBytes. I then opened the compressed image in "Preview" and then exported the image but I could not get below 740kBytes. Therefore, until I find out how to compress my photos to 300kBytes, the photos will have to wait.
Success with one more image!
Here is the 633W model and type plate
- Marconi 633W - model and type plate (292 KB)