Tube Dampeners for the Detector Stage

The short article about pot metal problems in the Kolster 6D and others is at the bottom of the page for the 6-D "Long Escutcheon" model at Radiomuseum.org. The article is in German. You will have to hit "translate" in your browser to get a fairly good rendition in English. Hope this helps.
Rod  WB6FBF

Thanks Chas. Die cast pot metal was used for so many electro-mechanical assemblies back in the 1920s that it can be hard to avoid. Yes. I was thinking had it been possible to do a local pickup for the Kolster 6D that a lot of grief could have been avoided. I got interested in it partly for its interesting single dial tuning control with its 3 stages of RF amplification but mainly because of the overall amazing condition. It appeared to have never been installed and used. Almost like out of the original box as evidenced by the excellent (and unused) power cable. 

The Radio Museum is a good source for information on a wide variety of radios and related equipment. There is a general search box at the top of each page where the item you are interested in can be entered and hopefully you will get some results on your item. Some times only a few results will come up and other times way too many so it will necessary to refine your search. Wording of your search request is very important as usual to getting good results. There is also a more specific search option available further down the page where you have to enter the category for the search engine to look in. This can save some time for example, if a tube type is wanted, it may be better to search for it only in the "Tube" section. 

The Radio Museum is an online radio club. I am not currently a member so I only have "Guest" privileges and this limits what you can see there. I do not know if you could enter "pot metal problems" in a search box and get a list of radios and speakers that used pot metal parts in their construction. Typing in "Kolster 6D" or "Kolster 6-D" in the search box at the top of any page will present you with a small list of entries on the set. For example: there was an early and late model of the 6D as identified by the escutcheons used. The differences are mostly minor but still significant. The late model version is a 1927 model while the earlier one is more closely reflective of 1926 production. At the bottom of the page for the Kolster 6-D (long escutcheon) is an article covering the pot metal problems in the 6D but it also mentions in a general way that the pot metal problem is wide spread. (The article is in German. You will have to hit translate in your browser for English). 

I am not sure what to do about repairs for the Kolster 6D. The cabinet needs work i.e. the back panel has separated from the sides at the top on both ends. Some wood clamps would probably be needed to get that back together again with the sides (carefully). The cross piece of wood in front under the lid (that covers the 4 gang tuning condenser) has also come loose on the left side. This cross piece is currently a bit fragile looking and I am afraid that more handling could cause the other side to come loose as well. The chassis itself is quite heavy and difficult to move around for inspection, etc..

After yesterdays inspection of the underside of the chassis, I am bit doubtful about getting it going for general use. However, some of what I saw was good as for example the wiring was very good and the audio transformers are still good as are the wirewound resistors. Overall construction quality is very good.

I am not a machinist nor do I have access to a machine shop. So I am not sure what to do about the broken pot metal controls. If I could fire it up for a test I think I would be happy with that. Years ago, there was a fellow that had experience with die casting and after retirement he set up a shop to produce castings for the radio hobby. That was Keith Perry. I sent him an order for a new casting for an AK horn speaker I had at the time. Sadly, he passed away about the time that I sent in the order.

73, Rod  WB6FBF

Rod,

Sorry to here about the combination of poor packing and the pot metal...

I have been fortunate the many of the radios I have with questionable pot metal parts I acquired locally and were either free or for small money, like $10...

I have not explored RM but I will ask. Can the site be mined for specific data if it has been entered into a radio description as to pot metal problems?

If not certainly the radio community could compile the encounters with the problem and create a list of these sets. The purpose would help collectors who cannot manage such repairs or in some cases the radio cannot be repaired if the failures are that extensive. For example the Radiola 44...  chas

A Kolster Installation Booklet (25 pages) that came with the 1927 Kolster 6D table radio I got in here yesterday stated that one of those weighted (i.e. heavy) tube caps was supplied as standard equipment with the radio for use on the Detector tube (as needed) to prevent "howling". I saw one of these caps for sale recently but it has since been sold. I was too slow with the clicker that time hi, hi. 

The Kolster 6D (late model) as received has shock (spring) mounted sockets installed for both the Detector and 1st Audio Stages. 

Not sure when I might get the set going. There was some serious damage to the cabinet. A quick check of the front panel controls suggest damage to the antenna peaking control and to the large, heavy tuning dial and 4 gang condenser. The whole tuning assembly appears to have shifted to the right in shipping.

The tuning dial is now jammed at about "30" on the dial. The tuning control itself is not turning at all. I was aware that some pot metal was used in constructing the set, notably in the tuning dial. Two of the three front panel controls also use pot metal for their construction. You can see pictures of them and the complete Kolster 6D at www.radiomuseum.org. Problems related to the manufacturer's use of pot metal parts in the 6D (and other sets) are documented there also at the bottom of the page.

73, Rod  WB6FBF
P.S. I have the chassis out of the cabinet now and have found that the center tuning control and left hand peaking control are shot due to broken and cracked pot metal. 
Rod

chas wrote:

There are many reasons for howling feedback:

Speaker too close to the radio, acoustical feedback.

Antenna/ground leads to close to detector in the receiver.

Not neutralized in a neutrodyne or Browning-Drake receiver.

Monophonic tube(s)

Improper used of regeneration controls.

Leaking or missing "B" bypass capacitors.

And often overlooked power source(s) that have a high impedance. For example the use of transistor 9 volt batteries as a B source. Too long or poorly routed battery power connecting wires/cable.

In home made sets it can be improper wiring techniques such as adjacent grid/plate leads.

The use of modern audio transformers that have low resistance therefore do not provide a sufficient plate load.

In thoriated tubes operating the tube without bias when required, with excessive B+ or dramatically reduced B+ either of which will cause operation outside of the normal curve and deplete the thorium at a faster rate.

Operation of the grid leak detector with a very high grid leak value combined with excessive plate voltage.

All of these issues are addressable and most can be easily corrected.

On very early receivers, the coil forms absorb moisture from many years, spoiling the "Q" of the receiver, the modern user will compensate by using excessive voltage in an attempt to get volume where-in the losses are in the coils forms.

Actual defects in connections such as poor solder joints or poor mechanical joints, even if they look good, re-solder or loosen, wiggle and re-tighten...  chas

Those are very helpful troubleshooting tips. THANK YOU

There are many reasons for howling feedback:

Speaker too close to the radio, acoustical feedback.

Antenna/ground leads to close to detector in the receiver.

Not neutralized in a neutrodyne or Browning-Drake receiver.

Monophonic tube(s)

Improper used of regeneration controls.

Leaking or missing "B" bypass capacitors.

And often overlooked power source(s) that have a high impedance. For example the use of transistor 9 volt batteries as a B source. Too long or poorly routed battery power connecting wires/cable.

In home made sets it can be improper wiring techniques such as adjacent grid/plate leads.

The use of modern audio transformers that have low resistance therefore do not provide a sufficient plate load.

In thoriated tubes operating the tube without bias when required, with excessive B+ or dramatically reduced B+ either of which will cause operation outside of the normal curve and deplete the thorium at a faster rate.

Operation of the grid leak detector with a very high grid leak value combined with excessive plate voltage.

All of these issues are addressable and most can be easily corrected.

On very early receivers, the coil forms absorb moisture from many years, spoiling the "Q" of the receiver, the modern user will compensate by using excessive voltage in an attempt to get volume where-in the losses are in the coils forms.

Actual defects in connections such as poor solder joints or poor mechanical joints, even if they look good, re-solder or loosen, wiggle and re-tighten...  chas

No. I haven't tried that. That's a new wrinkle to an old problem, hi, hi. Once the oscillations build up in these 1920s battery sets, it is hard to stop short of cutting off the power one way or another. Feedback from the loud speaker to the Detector Stage appears to be the main trouble. I should investigate to see what happens with headphones versus Loud Speaker operation. Just might give your suggestion a try out too. Thanks.
Rod  WB6FBF

Have you tried one suggestion I found, it was wrapping solder around the tube as it's heavy enough to stop vibrations and howling?

Has anyone had experience using those heavy, metal 1920s tube caps (Tube Dampers, Dampeners) on 201A type tubes to stop howling and feedback? I have run into this problem mostly with receivers that use a standard type socket for the Detector Stage. Sets that use a spring or shock mounted socket are much less likely to have the problem. For now, I have been trying to select the least microphonic tube for the Detector Stage in the sets that I have been trying out.
73, Rod  WB6FBF