I had a couple of questions and googling didn't help me come up with answers.
1) I've been told that the paper sleeves over can type power supply capacitors is there because the housing of the capacitor can be hot. Is this sometimes true? Often?
2) I know that one should not operate a tube amp without a load (i.e. speakers). Does this still hold true if you don't have any power tubes in the amp?
1) I've been told that the paper sleeves over can type power supply capacitors is there because the housing of the capacitor can be hot. Is this sometimes true? Often?
2) I know that one should not operate a tube amp without a load (i.e. speakers). Does this still hold true if you don't have any power tubes in the amp?
Without power tubes there is no current flow through the output transformer.
Therefore, there is no risk to the output transformer, and it is acceptable to apply power for testing in this configuration.
Caviat - since the power supply is now unloaded, voltages will be higher than if tubes were installed. In a marginal design, this can lead to failure of the HV filter capacitors.
Therefore, there is no risk to the output transformer, and it is acceptable to apply power for testing in this configuration.
Caviat - since the power supply is now unloaded, voltages will be higher than if tubes were installed. In a marginal design, this can lead to failure of the HV filter capacitors.
A can type capacitor should not be hot in the temperature sense, otherwise it is not long for this world.
In many cases the outer case is connected to the negative terminal and the chassis, so should not be 'hot' from a voltage point of view either. However, this is not always the situation so the case is insulated. Usually by plastic, not paper.
In many cases the outer case is connected to the negative terminal and the chassis, so should not be 'hot' from a voltage point of view either. However, this is not always the situation so the case is insulated. Usually by plastic, not paper.
Cardboard insulated FP style cans were very common on US hifi gear and were often found in late tube era amps using full wave solid state voltage doublers such as found in the Harman Kardon Citation II and V, and IIRC some late Fisher tube power amps. HH Scott used FP cans with a positive case polarity (reverse of standard cap) in bias and filament supplies and these were sometimes covered with a cardboard case as well.
Plastic sleeves were not widely used here on FP style cans in my limited experience, in fact in that time frame American axial electrolytics frequently used cardboard sleeves. Japanese and European capacitor manufacturers embraced plastic sleeves a lot earlier IMLE..
Plastic sleeves were not widely used here on FP style cans in my limited experience, in fact in that time frame American axial electrolytics frequently used cardboard sleeves. Japanese and European capacitor manufacturers embraced plastic sleeves a lot earlier IMLE..
1...If the can is isolated from the chassis then it has the potential to become live..the can in most cases is negative or isolated internally..so if there is a metal can it should be at earth if exposed. Also be aware that a negative connection is not always negative Gnd. If its hot (temp) its going to blow out at some point. (Be wary of any metalwork that is not at Earth potential)
2...If you remove power tubes then ok the output section is not working, however there will be no load on the HT so it could go high value and take out the PSU caps if the rating is exceeded...also if you remove some preamp tubes be careful they are not DC coupled.. you could blow coupling caps if they are old..
NB I guess you already know it should have an isolation Tx..
Regards
M. Gregg
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.