Hi audio lovers ! I bought an amplifier from a Rockola 429, the chassis is 41056-A. The tubes I got with were very bad sounding so I got some new output tubes. The problems are the basic hum and the lack of treble. Even if I put the treble at maximum, it is still not enough compared to my other amps. Does someone have some advices for improving the sound, because right now my only option is to sell it. Maybe chage all the caps , they seem to be all original (1965). Or modify the circuit, or use all the transformers and tubes, get a modern schematic and redo it entirely.
Before you do all that how do you know that the output transformer is up to hi-fi standards ?
The parts aren't cheap to renovate it but changing the capacitors could be tried first especially the inter-stage coupling capacitors ,its always a good idea to change them first for high quality modern film versions.
The parts aren't cheap to renovate it but changing the capacitors could be tried first especially the inter-stage coupling capacitors ,its always a good idea to change them first for high quality modern film versions.
You're right about the OPTs. I have some other that are good for push-pull 25W , I could try them to compare. Thank you for your comments.
Rather than guessing or replacing parts at random, you should look at the schematic (which you didn´t care to supply 🙄)
If you had, you would have noticed its weird tone control section: "almost normal" Bass boost/cut but treble is incomplete: cut only.
Best is "flat" with Treble on 10 which is not enough.
Replace that tone control with a standard Hi Fi type passive one, often called "Baxandall" but which is actually a "Johnson" type.
You will then recover full control over Bass and Treble, and at the proper frequencies.
"Sound is 99% on the circuit and 1% in the parts"
Attachments
And just changing an output transformer with another model and not adjusting the negative feedback parts might be interesting . . . .
because negative feedback combined with the phase and frequency response differences of different output transformers might create an oscillator.
because negative feedback combined with the phase and frequency response differences of different output transformers might create an oscillator.
Please consider that this amplifier never was intended to be HiFi, but for sitting in a jukebox instead, feeding - mostly cheap - full range speakers with the primary capability of being as loud as possible. Hence it can't be exluded that it won't fit your needs.
Best regards!
Best regards!
Thank you very much for help. I wouldn't have noticed how bad is the tone control due to limited experience in that field. I'll try to figure how to modify the tone section.
Steber,
In this case, you are the "marketing" person who tries to define and produce a product with features that more customers will buy . . . and you are the only customer.
There are lots of customers who purposely purchase Hi Fi systems that do not have tone controls; and for other customers, there are products that have a tone control bypass switch.
For a number of Hi Fi aficionados, They merely say: "Who needs a tone control?"
In this case, you are the "marketing" person who tries to define and produce a product with features that more customers will buy . . . and you are the only customer.
There are lots of customers who purposely purchase Hi Fi systems that do not have tone controls; and for other customers, there are products that have a tone control bypass switch.
For a number of Hi Fi aficionados, They merely say: "Who needs a tone control?"
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