It is currently Mon Mar 16, 2020 11:10 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 33 posts ]  Go to page Previous  1, 2, 3  Next
Go to page Previous  1, 2, 3  Next
Author Message
Post subject: Re: Hot Rod Deluxe-BIAS voltage is 6.8mV only (distorted cle
Posted: Mon Oct 07, 2013 2:54 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
6 years olds , replace all tubes. They are not working as your reading show.


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: Hot Rod Deluxe-BIAS voltage is 6.8mV only (distorted cle
Posted: Mon Oct 07, 2013 4:02 pm
Offline
Hobbyist
Hobbyist
User avatar

Joined: Mon Oct 07, 2013 1:39 am
Posts: 16
Location: EU - Croatia
Well, it can't hurt to replace all the tubes :? after all, six years looks like long enough to deplete them. :roll:

How about this tubes... this can be found in a store near me :

JJ-ELECTRONIC 6L6GC (PAIRED)
JJ-ELECTRONIC ECC83S (12AX7)


Top
Profile
Post subject: Re: Hot Rod Deluxe-BIAS voltage is 6.8mV only (distorted cle
Posted: Tue Oct 08, 2013 1:06 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
FingerprintCrewPlayer wrote:
Well, it can't hurt to replace all the tubes :? after all, six years looks like long enough to deplete them. :roll:

How about this tubes... this can be found in a store near me :

JJ-ELECTRONIC 6L6GC (PAIRED)
JJ-ELECTRONIC ECC83S (12AX7)


Good tubes, I use them . You probably do not need the ECC83's


Top
Profile
Post subject: Re: Hot Rod Deluxe-BIAS voltage is 6.8mV only (distorted cle
Posted: Tue Oct 08, 2013 4:22 am
Offline
Hobbyist
Hobbyist
User avatar

Joined: Mon Oct 07, 2013 1:39 am
Posts: 16
Location: EU - Croatia
Great to hear that JJ-ELECTRONIC 6L6GC are good. I was thinking to replace all the tubes. After all, with 6 years of use... so... you think that preamp section tubes V1-V2 and V3/PI are OK... do not need to change them?

I found only ECC83S near me ... and as far as I can see, they are actually the same as 12AX7. http://www.jj-electronic.com/pdf/ECC%2083%20S.pdf

JJ 6L6GC http://www.jj-electronic.com/pdf/6L6%20GC.pdf

Many thanks for advice! :D


Top
Profile
Post subject: Re: Hot Rod Deluxe-BIAS voltage is 6.8mV only (distorted cle
Posted: Tue Oct 08, 2013 4:38 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
I would replace V3 , 12AX7 / ECC83 (same) Phase inverter tube work hard too . Not V1, V2

Replace 6L6's too. And check / adjust bias with these new 6L6


Top
Profile
Post subject: Re: Hot Rod Deluxe-BIAS voltage is 6.8mV only (distorted cle
Posted: Wed Oct 09, 2013 10:21 am
Offline
Hobbyist
Hobbyist
User avatar

Joined: Mon Oct 07, 2013 1:39 am
Posts: 16
Location: EU - Croatia
Got today paired JJ 6L6GC output tubes and all three V1/2/3 ECC83S (12AX7A). Did replaced them all but no luck... only one difference I do see now, there is some Rmmmmmmmm noise at the loudspeaker (all pots including DRIVE and VOLUME are set to zero)... so, this has to be something else. With old tubes there is no Rmmmm noise. I measured the BIAS voltage, it is still very, very low, about 5,8mV - 6mV ... I measured B+ on C31 respect to ground... i got +366VDC. On output tubes the voltages on pin 4 and pin 3 are almost the same. At pin 4 I got +389VDC. At pin 3 i got +390VDC. :(


Top
Profile
Post subject: Re: Hot Rod Deluxe-BIAS voltage is 6.8mV only (distorted cle
Posted: Wed Oct 09, 2013 10:31 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
Check and tightened 6L6 's socket connectors , you have to know how to not damage connector . You tube ? Check 6L6 tubes ground.

Something you did not read well with your meter or did not see. I have to read all the post from the beginning to know where something wrong :(


Top
Profile
Post subject: Re: Hot Rod Deluxe-BIAS voltage is 6.8mV only (distorted cle
Posted: Wed Oct 09, 2013 10:47 am
Offline
Hobbyist
Hobbyist
User avatar

Joined: Mon Oct 07, 2013 1:39 am
Posts: 16
Location: EU - Croatia
All the tubes are tightened, including 6L6 output tubes of course. I checked that twice. Everything seems OK. On BIAS-ing resistor R66 I read 1.7 ohms.


Top
Profile
Post subject: Re: Hot Rod Deluxe-BIAS voltage is 6.8mV only (distorted cle
Posted: Wed Oct 09, 2013 11:09 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
I'm sure you do your best but IMO something is not well connected , not good contact or broken printed circuit around your 6L6's and you don't see it.

Or your reading are wrong .

This amp is not easy to work on. Some picture of 6L6 circuit might usefull


Top
Profile
Post subject: Re: Hot Rod Deluxe-BIAS voltage is 6.8mV only (distorted cle
Posted: Wed Oct 09, 2013 11:32 am
Offline
Hobbyist
Hobbyist
User avatar

Joined: Mon Oct 07, 2013 1:39 am
Posts: 16
Location: EU - Croatia
As far as I can see, printed board for tubes is more than OK... there is no sign of any broken printed circuit line ... I could not find any bad soldering point also. :?

http://s24.postimg.org/ot8oxmgut/FENDER_DSC01204.jpg


Top
Profile
Post subject: Re: Hot Rod Deluxe-BIAS voltage is 6.8mV only (distorted cle
Posted: Wed Oct 09, 2013 12:45 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
Better to see a qualified tech .


Top
Profile
Post subject: Re: Hot Rod Deluxe-BIAS voltage is 6.8mV only (distorted cle
Posted: Wed Oct 09, 2013 4:55 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
You should really check out why your DC supply is so low, that is not normal, and could be the key to your issue, assuming that your meter is good. Have you tried another meter to make sure your readings are correct?

The reading on R66 of 1.7 ohms will give you an unexpected measure of the bias current, but not by a factor of 10, as you indicated your reading is 6.8 mV. Just take the voltage drop measured across the resistor, divide by the measured resistance, and that is the current through the resistor (in your case that would be 4 mA). Mine measures 1.2 ohms, and I always calculated using 1.2 ohms, but now I use bias probes and skip the resistor measurement.

It is really hard to believe that you only have 4 mA of current through both output tubes. Considering that many readings that you have are off in some way, I would first verify your meter, compare the reading to another meter. If you verify that the meter is good, check your amp power supply and find out why the voltage is so low. Check the diodes, caps, solder connections, etc.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Hot Rod Deluxe-BIAS voltage is 6.8mV only (distorted cle
Posted: Wed Oct 09, 2013 5:06 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
BTW, you might want to get a capacitance meter. You can get an inexpensive Tenma brand and they are decent. I like to have at least two of many of my meters, one for the shop and one for service calls. I recently picked up this Tenma LCR meter for service calls and found it to very decent and it works quite well.

http://electronics.mcmelectronics.com/search?p=R&srid=S8-UKLD02&lbc=mcmelectronics&w=capacitance&url=http%3a%2f%2fwww.mcmelectronics.com%2fproduct%2f72-8155&rk=8&uid=936021516&sid=2&ts=custom&rsc=9wW1mvTLF39ZxhJ%3a&method=and&isort=score&view=list

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Hot Rod Deluxe-BIAS voltage is 6.8mV only (distorted cle
Posted: Thu Oct 10, 2013 2:13 am
Offline
Hobbyist
Hobbyist
User avatar

Joined: Mon Oct 07, 2013 1:39 am
Posts: 16
Location: EU - Croatia
I did all readings with another multimeter... the changes in reading are really the minor ones. The voltages without tubes (all 5 tubes pulled out) are high.

So I did recheck the voltages with other multimeter, and with all tubes pulled out, the AC voltage between points CP11 and CP12 with standby switch open is 337V AC. With standby switch on, point B+ (voltage across capacitor C31) is 448VDC. I think this is OK.

After inserting the tube V1 (new ECC83S tube), the voltage on B+ drops to 424VDC. The same happens when V2 is inserted B+ is 424VDC... the voltage is still the same when V1 and V2 are inserted, I measured again = 424VDC. But, when V3/PI is inserted, the B+ goes down to 412-413VDC. On 'C-' point the reading was -49VDC. On resistors R78 and R79 I got +17/-16VDC and on the other sides of the resistors R78/79 the voltage is +48/-49VDC. :|

On output tubes the voltages on pin 4 and pin 3 are indeed almost the same. At pin 4 I got +389VDC. At pin 3 i got +390VDC. Resistors R61 = 465 and R62 = 466 ohms.

I rechecked resistor R R66... the reading is between 1.7 and 1.1 ohms... it really depends how strong you apply the multimeter probe wires to soldering spots.

And yes, to say it again, with all new tubes in, I got that 'Rmmmmmmmmm' sound... with old tubes, this was not the case.

Idea is to change all resistors in PI and output stage, just in case... to name : R64/65, R57/58, then R59/60 and R61/62.


Top
Profile
Post subject: Re: Hot Rod Deluxe-BIAS voltage is 6.8mV only (distorted cle
Posted: Thu Oct 10, 2013 2:44 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
"......I rechecked resistor R R66... the reading is between 1.7 and 1.1 ohms... it really depends how strong you apply the multimeter probe wires to soldering spots. "

Answer ; this is because your test point are not in good contact , there some oxidation on solder you have to go trought to have real good reading .
___________________________________________
"....After inserting the tube V1 (new ECC83S tube), the voltage on B+ drops to 424VDC. "

Answer ; an only one ECC83 can't drop B+ . Something wrong there.



I dont blame you but your lack of knowledge and experience is a real problem to help you. Sure there are many error you do when your tests.


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 33 posts ]  Go to page Previous  1, 2, 3  Next
Go to page Previous  1, 2, 3  Next

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: