10-03-2017, 02:02 PM
I know this question has been discussed here as well as in other antique radio forums. However I am not finding the same results that others have had and I post here in the hopes someone can point me to the error in my ways. The output transformer on my 41-300 had an open primary. I had a donor chassis, and that transformer was good from center tap to one side. The DC resistance measured 320 ohms on that winding.
I bought the Hammond 125E transformer which I was told is what others were using but it sounds terrible on my radio. All of the base tones are washed out and the output sounds cheap and tinny. However I own a Zenith speaker and output transformer which I tried and it sounds much better.
The only difference I have been able to find between the two is the Hammond transformer has about 125 ohms DC resistance on the primary winding but the Zenith output transformer has 580 ohms DC resistance on the primary winding. Here I am looking only at the DC resistance and not the overall impedance of that speaker output circuit. I have not checked the turns ratio on the Zenith output transformer.
FWIW I have grounded the tone and volume controls that previously attached to the center tap of the output winding on the original Philco output transformer. I had used various combinations on the Hammond transformer without different results.
I determined that the solution is to find a transformer that has between 550 ohms and 700 ohms DC resistance on it's primary winding as that seems to solve the problem. But I'm posting here in the hopes that someone may see something in that amplifier/output circuit that I have missed which could be the cause. I don't get it how others use the Hammond transformer and have it work well while it doesn't work well on this one. I have checked and rechecked the hook up, switching between plates to the primary and I have used all of the various output combinations, but nothing seems to improve the performance until I use a transformer with a higher DC resistance on the primary.
I don't think I am asking too much from this radio, I have others that are older and they sound much better. I would accept the quality of sound I get from the Zenith speaker but to be honest I had greater sound expectations for this radio.
The Zenith speaker and output transformer that works best is a model 7S685, Rider's 13-30. The speaker part number is 49-475. On the outside of the transformer is stamped 9448 7.
Thanks for any help.
Tomie
I bought the Hammond 125E transformer which I was told is what others were using but it sounds terrible on my radio. All of the base tones are washed out and the output sounds cheap and tinny. However I own a Zenith speaker and output transformer which I tried and it sounds much better.
The only difference I have been able to find between the two is the Hammond transformer has about 125 ohms DC resistance on the primary winding but the Zenith output transformer has 580 ohms DC resistance on the primary winding. Here I am looking only at the DC resistance and not the overall impedance of that speaker output circuit. I have not checked the turns ratio on the Zenith output transformer.
FWIW I have grounded the tone and volume controls that previously attached to the center tap of the output winding on the original Philco output transformer. I had used various combinations on the Hammond transformer without different results.
I determined that the solution is to find a transformer that has between 550 ohms and 700 ohms DC resistance on it's primary winding as that seems to solve the problem. But I'm posting here in the hopes that someone may see something in that amplifier/output circuit that I have missed which could be the cause. I don't get it how others use the Hammond transformer and have it work well while it doesn't work well on this one. I have checked and rechecked the hook up, switching between plates to the primary and I have used all of the various output combinations, but nothing seems to improve the performance until I use a transformer with a higher DC resistance on the primary.
I don't think I am asking too much from this radio, I have others that are older and they sound much better. I would accept the quality of sound I get from the Zenith speaker but to be honest I had greater sound expectations for this radio.
The Zenith speaker and output transformer that works best is a model 7S685, Rider's 13-30. The speaker part number is 49-475. On the outside of the transformer is stamped 9448 7.
Thanks for any help.
Tomie
