Hi i have a tube amplifier that's playing up making my speakers cut in and out i want to just try and identify the problem by going in with a multimeter and testing the values across the components (look for a possible capacitor discharging).
Would i be able to remove all the the tubes and turn it on? Obviously with the speakers still connected.. (I'm not that stupid)
Also... Any ideas as to what could be causing the amp to cut out every 3 seconds? ... it does it on both channels but at different intervals. It doesn't do it straight away when you turn amp on, but a minute later and the pads of speakers move in and out strangely.
The amp is a Unisis from TubeTechnology. It has the Prophet Pre-Amp aswell.
Anyway..
Thanks guys <3
,
Cogline
Would i be able to remove all the the tubes and turn it on? Obviously with the speakers still connected.. (I'm not that stupid)
Also... Any ideas as to what could be causing the amp to cut out every 3 seconds? ... it does it on both channels but at different intervals. It doesn't do it straight away when you turn amp on, but a minute later and the pads of speakers move in and out strangely.
The amp is a Unisis from TubeTechnology. It has the Prophet Pre-Amp aswell.
Anyway..
Thanks guys <3
,Cogline
Thank you so much for quick replies, can't find any schematics about! very frustrating...
All i can show you is
http://www.tubetechnology.co.uk/ds/ds_uni_power.pdf
I'll look for some bad solder joints still need to know if i can operate my tube amp without any tubes inserted.
Cogline
All i can show you is
http://www.tubetechnology.co.uk/ds/ds_uni_power.pdf
I'll look for some bad solder joints still need to know if i can operate my tube amp without any tubes inserted.
Cogline
Bad contact of some sort such as Indiana Joes' bad solder joint would be high on my hunch list.
If both speakers are cutting out and in together then it would seem the fault must be in a component common to both channels. The trick in fault finding is to narrow down its whereabouts using careful analysis. Intermittent faults are much harder to track down than a constant fault.
If both speakers are cutting out and in together then it would seem the fault must be in a component common to both channels. The trick in fault finding is to narrow down its whereabouts using careful analysis. Intermittent faults are much harder to track down than a constant fault.
Last edited:
Glad your all keen to help me!
okay so I'll give you the process which occurs.
So i turn on my pre-amp, leave it for a min then turn on my amplifier. the problem does not occur straight away but instead kicks in about a minute or sometimes longer later. When i turn the amplifier back on after being on not long ago (so it's still a bit hot) the problem occurs STRAIGHT away.
The speakers will cut in and out from channel to channel every 2-3 secs. they do not cut out in sync but one after another so there is always sound coming out of one of the speakers. while this is happening the pad on the speakers are continuously moving in and out as if producing a low frequency sound. This however does happen at the same time.
The amp is about 15 years old. I obtained it from the previous owner who said something had "blown in it" on the last use. sure enough one of the front power tubes was smashed.
So it works PERFECT for a few mins. So surely no massive damage has been done?
Thank you,
Please ask if further info needed.
Cogline
okay so I'll give you the process which occurs.
So i turn on my pre-amp, leave it for a min then turn on my amplifier. the problem does not occur straight away but instead kicks in about a minute or sometimes longer later. When i turn the amplifier back on after being on not long ago (so it's still a bit hot) the problem occurs STRAIGHT away.
The speakers will cut in and out from channel to channel every 2-3 secs. they do not cut out in sync but one after another so there is always sound coming out of one of the speakers. while this is happening the pad on the speakers are continuously moving in and out as if producing a low frequency sound. This however does happen at the same time.
The amp is about 15 years old. I obtained it from the previous owner who said something had "blown in it" on the last use. sure enough one of the front power tubes was smashed.
So it works PERFECT for a few mins. So surely no massive damage has been done?
Thank you,
Please ask if further info needed.
Cogline
No probs, just trying to eliminate other faults such as incorrect tube type, incorrect bias, internal damage due to being dropped for instance by previous owner. If after replacing tubes it ran properly for a reasonable time then we have a platform to start from.
PS. just as an after thought, does your model have a stereo/mono switch and if it does what effect does it have.
PS. just as an after thought, does your model have a stereo/mono switch and if it does what effect does it have.
Last edited:
From the linked data sheet, it appears that it's SS rectification, and from the OP's previous post, it sounds like the fault is repeatable once the amp is warmed up.
Cogline: Are you comfortable working around high voltage? This amp probably runs a B+ voltage of around 300-350VDC. Have you read the safety sticky at the top of this forum? Do you have clip leads for your DMM? Clip leads make troubleshooting "hands-off" which is much safer than probing a live amp with a regular meter probe tip. Are you aware that you need to keep one hand in your pocket (or around your back) when troubleshooting a live amp?
Cogline: Are you comfortable working around high voltage? This amp probably runs a B+ voltage of around 300-350VDC. Have you read the safety sticky at the top of this forum? Do you have clip leads for your DMM? Clip leads make troubleshooting "hands-off" which is much safer than probing a live amp with a regular meter probe tip. Are you aware that you need to keep one hand in your pocket (or around your back) when troubleshooting a live amp?
Last edited:
1st inspect innards - any visible damage, discolored parts, shorts, scratches, loose wires, loose strands, connectors etc
2nd disconnect pre-amp and short the power amp input terminals - any change ?
next I would be concerned about speaker cones moving in and out - you could damage your speakers on the long run - use a dummy load (resistor) instead and hook up a meter
dummy load is not necessaryily to be 8 ohms, I would possibly try 100 ohms to begin with.
now you can safely proceed with in-circuit measurements - start with power rails, are they stable and reasonable value ? !!! be careful - dangerous high voltage everywhere !!!
one source talks about "... individual output tube protection" audiocostruzioni.com
might give rise to cutting-in/out if defective or indicate overload or short or ...
pull tubes of one channel - any change in the remaining channel
same vice-versa
is there a bias pot ? make shure it hasnt been set to one end by the pre-owner
to be cont'd ...
2nd disconnect pre-amp and short the power amp input terminals - any change ?
next I would be concerned about speaker cones moving in and out - you could damage your speakers on the long run - use a dummy load (resistor) instead and hook up a meter
dummy load is not necessaryily to be 8 ohms, I would possibly try 100 ohms to begin with.
now you can safely proceed with in-circuit measurements - start with power rails, are they stable and reasonable value ? !!! be careful - dangerous high voltage everywhere !!!
one source talks about "... individual output tube protection" audiocostruzioni.com
might give rise to cutting-in/out if defective or indicate overload or short or ...
pull tubes of one channel - any change in the remaining channel
same vice-versa
is there a bias pot ? make shure it hasnt been set to one end by the pre-owner
to be cont'd ...
Lot of information, firstly to answer questions :
I am very aware of the dangers of tinkering with live amps and even ones not connected to a power supply. I am equally aware of easy precautions that are to be taken in order to avoid shock. Thank you for your concern though.
The tubes are definitely the correct types and I'm pretty sure they are bias correctly since I'm using the tubes that came with the amp originally.
Looking inside the amplifier no damage can be seen.. no weak solder joints no dis-colored components everything looks good.
"pull tubes of one channel" - are you sure this is safe to do won't this increase the load on the other channel?
I'll look into the information and troubleshooting tomorrow (tired and need some natural light to help see into the amp a bit better!).
Lastly, i am the only person after being manufactured to have taken a look into the amplifier so the bias is at factory Default and nothing has been changed.
once again thank you!
I am able to take pictures if needed just ask!
Cogline
I am very aware of the dangers of tinkering with live amps and even ones not connected to a power supply. I am equally aware of easy precautions that are to be taken in order to avoid shock. Thank you for your concern though.
The tubes are definitely the correct types and I'm pretty sure they are bias correctly since I'm using the tubes that came with the amp originally.
Looking inside the amplifier no damage can be seen.. no weak solder joints no dis-colored components everything looks good.
"pull tubes of one channel" - are you sure this is safe to do won't this increase the load on the other channel?
I'll look into the information and troubleshooting tomorrow (tired and need some natural light to help see into the amp a bit better!).
Lastly, i am the only person after being manufactured to have taken a look into the amplifier so the bias is at factory Default and nothing has been changed.
once again thank you!
I am able to take pictures if needed just ask!
Cogline
Good point! Cogline: Do you happen to know the impedance of your speakers? Or even better, an impedance curve?
Is there any evidence of the output tubes "red plating" when the amp is warmed up? Have you checked the bias? Setting/verifying that the bias is set correctly would be the first thing I would do.......
Last edited:
Yes my speakers are Sonus Faber Electa 8 ohms! very nice i play them with a SS amp i have.
I'm completely lost with this comment "one source talks about "... individual output tube protection" audiocostruzioni.com
might give rise to cutting-in/out if defective or indicate overload or short or ..."
Care to explain?
Thanks,
Cogline
I'm completely lost with this comment "one source talks about "... individual output tube protection" audiocostruzioni.com
might give rise to cutting-in/out if defective or indicate overload or short or ..."
Care to explain?
Thanks,
Cogline
If your speaker's impedance drops to very low levels at some freq (not too uncommon) or your bias adj is not set correctly, you may be pushing the output tubes too hard and causing the protection circuit to kick in. Tube amps typically have higher output impedance than SS amps and like a relatively flat impedance curve for a speaker load.
From the linked pics, it appears that the bias adj pots are located on the top deck.....easy enough for anyone to tinker with.....
Do you have any other speakers that you can use with this amp?
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.