• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

845 set bias.

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mcnaget

Member
Joined 2013
845 set

Rod Coleman said:
I believe that the extra components have been added to the filament terminals to try to control the noise and humm, which is likely, when only a raw dc supply is used.

You could improve the raw dc supply, to make it reliable, and quieter. you will need much bigger capacitors, and some series filtering.

This can lead to a quieter system, but problems will remain:

- the variation of filament voltage follows the mains tolerance, plus drops in the house. For example UK mains is allowed +/- 10%. this is enough to shorten the life of 845s. It's better to keep the voltage at 2-5% of the nominal 10V.

- the raw dc supply will allow some part of the rectifier recharge, and reverse recovery pulses.
- the electrolytic will short out the signal across the filament.

These last two problems will degrade the sound. You can find a better solution with a "CCS filament regulator" - which blocks the rectifier noise/current pulses and presents high impedance to the filament. With a CCS filament regulator, you remove the extra parts, which are only to try to fix a bad solution!
Click to expand...

Could you explain what are the purpose of those two braun capacitors rated 10V/4700uf is it safe to replace them vith higher voltage and capacitance.

thx
 
Rod Coleman

Rod Coleman

Member
Joined 2004
mcnaget said:
Could you explain what are the purpose of those two braun capacitors rated 10V/4700uf is it safe to replace them vith higher voltage and capacitance.

thx
Click to expand...


The capacitors, and the nearby bridge rectifiers are in a circuit like the one linked below.
It's just a raw rectified dc supply.

Full Wave Bridge Rectifier Supply | Micro Digital

If you upgrade the caps, you'll also need a upgraded bridge (that one looks too small). Increasing the cap value increases the rms current, and the stress on the rectifiers.

The caps need to be at least 2x 22000uF 25V, with a resistor between them to get the voltage to between 9.9 and 10.1V at normal line voltage (line tolerance will worsen the stability of the supply).


But really, this is could be a lot of work - only to stop it from burning out - the sound will be a long way from the possibilities of the wonderful 845
 
M

mcnaget

Member
Joined 2013
Bridge rectifier.

Rod Coleman said:
The capacitors, and the nearby bridge rectifiers are in a circuit like the one linked below.
It's just a raw rectified dc supply.

Full Wave Bridge Rectifier Supply | Micro Digital

If you upgrade the caps, you'll also need a upgraded bridge (that one looks too small). Increasing the cap value increases the rms current, and the stress on the rectifiers.

The caps need to be at least 2x 22000uF 25V, with a resistor between them to get the voltage to between 9.9 and 10.1V at normal line voltage (line tolerance will worsen the stability of the supply).


But really, this is could be a lot of work - only to stop it from burning out - the sound will be a long way from the possibilities of the wonderful 845
Click to expand...

THX for the answer you are meaning the small bridge rectifier the black square one that is to small , what value should be if i decided to upgrade this and capacitors?

Thanks again for helping me out.

regards
 
A

avp1

Member
Joined 2010
Tony714 said:
Need help with my brand new amp. It aound fine until i go to about 1/2 of the volume then it start rattle and sound is smear off, horrible sounding.
Click to expand...
You likely hit a clipping point. Volume setting does not matter in this case - it can be full volume or 1/3, all depend on how much power amp can produce. It does not mean that your amp is not broken though. Probably need to run full series of tests. Do you have signal generator and oscilloscope?
 
T

Tony714

Member
Joined 2014
First of all, thank you very for the link. I've been reading it and realize what it is. The clipping could come from any source. But i think it from the amp. Which i play same setup except for switch out the amp. Could not believe a $4600 amp would give me such problem.
 
kevinkr

kevinkr

Administrator
Joined 2004
kta-hifi.net
Paid Member
All amplifiers eventually run out of power regardless of cost. The position of the volume control has no relationship to the maximum power achievable and is solely a reflection of the output level of the source and the gain in the amplifier. For example a source with very high output voltage levels ("louder") would require a lower volume control setting for a given loudness than another component with a lower output level. The "louder" component would also cause the amplifier to clip at a lower volume setting than a "quieter" component.

A little more information might be helpful, the output rating of the power amplifier and any other details you can provide along with speaker information including efficiency. Finally are you in a large or small sized room.

Finally does it actually get loud enough before sounding bad?

Spending a lot of money on an amplifier unfortunately is no guarantee that it was competently designed.
 
A

avp1

Member
Joined 2010
Tony714 said:
Thank you for the info, here is my set up and spec
The amp is Hyperion HT-845
HT-845
I pair it with Mcintosh C-36
McIntosh Preamplifiers
And run a pair of PSB Stratus Gold
http://www.psbspeakers.com/content/110519132918-stratus_brochure.pdf
Click to expand...
With these speakers you can't expect really loud music from your amp. First thing would be to turn bass tone control in your preamp down a bit. Did you connect them to 4 ohms output? You may try 8 ohms output instead. But I would check that amplifier is working properly first - probably time to contact Hyperion service.
 
T

Tony714

Member
Joined 2014
Thx for your response, i never thought of hook it to 8 ohm, do to the dealer state that i need to connect it to the right ohm or i will damage the amp (is it true? ) Beside amp is brand new out of the box, play less than 30 hrs. They have 4,6 & 8 ohm connection. Is it safe if i connect to 8 ohm? Thx
 
A

avp1

Member
Joined 2010
Tony714 said:
Thx for your response, i never thought of hook it to 8 ohm, do to the dealer state that i need to connect it to the right ohm or i will damage the amp (is it true? ) Beside amp is brand new out of the box, play less than 30 hrs. They have 4,6 & 8 ohm connection. Is it safe if i connect to 8 ohm? Thx
Click to expand...
You may try both 6 and 8 ohms outputs. It is safe to connect speakers to any.
 
Celsius

Celsius

Member
Joined 2011
Parafeed813 said:
Since the filament of a directly heated valve is the cathode, anything that shows up there will end up on the speaker terminals. Therefore the heater supply needs to be very clean. Even ac sounds better than simply rectified and buffered with a large electrolytic.
I use a switching supply for the 10V/5A for my 813's. Small and efficient. Chassis cooling is enough for these regs.
Click to expand...

You don't have any noise with the switching supply, or have you need to increase the resistor of grid stoppers or ferrites ?
 
M

mcnaget

Member
Joined 2013
5R4GY

I got four of these on the back of my amp posted on first page they suposed to be used for heather im not sure next to those four tubes are one very large transfomer i dont know the value when the four tubes are inserted the transformer producing a hum or buzz if i pull them out trafo is silent are there any solution to that.

thx

regards
 
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