Allwave 23 IF alignment

[Thomas Day]

  Are there any detailed instructions for IF alignment other than those given in the Scott service manual? Would it have originally been done using a sweep generator to set the needed bandwidth? After the 1st of the year, I am going to go thru the chassis and perform a complete alignment procedure. The radio seems to be working well with a 53 foot roof top antenna, and all the bypass and coupling caps have been replaced, along with all the power supply caps, except for the line bypass caps in the power supply.Those are disconnected at the moment. I also have the copy of the checkout instructions that were posted here.

I am also interested in building the Volume Range Expander using more 'modern' tubes that have the same characteristics as the original tubes used.

Thanks

Thom

[Kent King]

Thom - I have always had great success aligning the AW23 following the Scott instructions closely. I use modern equipment which allows me much finer control on the values (frequency settings, voltages). I will try to post something here about the volume expander circuits, I wrote something years ago about it and if you want to build a similar unit, it might help.

Kent

[Norman S Braithwaite]

I am relatively certain that the Full Range High Fidelity receiver was shipped from the factory after sweep alignment or at least an equivalent alignment checking frequencies surrounding the center. The service data was written for typical well equipped service shops to maintain reasonable radio performance. When peak aligned as instructed by the Scott service data, the aprons of the IF bandpass characteristic toward the high fidelity end of the bandwidth control are not always equal and are sometimes very far from equal resulting in audible distortion of higher frequencies. I usually peak align per the Scott instructions then adjust the bandpass characteristic by slightly backing off the last couple IF adjustments while sweep aligning the IF near the high fidelity position. In some receivers the IF will actually oscillate if all stages are well peaked.

The volume range expander is only useful for reproduction of classical and operatic performances. It backfires on other forms of music.

Norman

[Bill Liers]

Thom, all,

 

I find many opinions on the subject of proper IF alignment. Nearly as many as the number of restorers consulted. I believe that for radios that you are going to listen to, swept alignment is important in order to maximize smooth response and minimize distortion as Norm mentioned. There is no end to the degree you can take it to though. One friend insists that the alignment should take into account the entire variable IF range in consideration of signal levels across the useable range. This of course takes considerable effort, however when I checked my prior swept alignment results while varying the input level, my results were sceud. Re-trimming improved this again, much to my surprise. I now allow at least a full day or two to align a Scott variable.

 

This is done after selecting tubes for noise contribution which takes a few hours in itself. If a tube is changed post alignment, it will have an effect. The result allows the set to perform as it was designed. I find that the "aged" tubes we use today have a greater noise and performance spread than when they were new. As far as factory alignment goes, I'd love to know exactly how it was done but imagine that it's like anything else, familiarity with the product and a production environment can speed things up considerably.

 

regards, Bill

[Thomas Day]

All:

Thanks for all the information. I am familiar with doing sweep alignments on FM sets, but never on an AM set. I spent about 7 years on the audio bench for Heathkit back in the late 60's thu 74. Got to work on all of the old tube and transistor tuners. I have a fairly accurate generator (not sweep) and a frequency counter, so I can get the IF to exactly 465. I also have a set of NOS 39/44 tubes to use as well. Heath had a pair of HP 202H generators for AM and FM. The later stereo receivers could be adjusted to have about 2 to 3 microvolts of FM sensitivity.  We didn't worry too much about the AM sensitivity, since most of these would not be used for DX. A plastic 'diddle stick' is probably a must, since there is B+ on the trimmers. 

As for the expander, it would be more of an experiment to see how it worked.  Not much music on the AM band, in fact only  a couple of stations in the Chicago area play music and all of it is rock or latino. 

Thom

[David C. Poland]

Thomas, 

Also - the RCA tube manual has a section of volume expander. For example, RC-19 it is on page 31. - Dave