Mailliw

Re-capping an old tube guitar amp (Riviera 725)
« on: July 23, 2005, 06:37:08 PM »
Hi,

I was given this working but very noisy tube guitar amp head. The can-caps on the top are stamped JUL '67. There is basically no info about it on the internet. It was made in Canada.

I drew up the circuit, it is very similar to a Fender Champ, but it has two 12AX7As whereas most champs only have one.

large schematic

small schematic

physical pictures:

top full
top 800x ...
bottom full
bottom 800x ...
bottom right full
bottom right 800x ...
bottom left full
bottom left 800x ...

I read that a lot of people replace 40-450s in Fender amps with spraque atoms, but they are ~5 each bucks at mouser. Would panaonic ecgs be fine? (~2.35 at digikey)

The blue/yellow 0.1uFs are Dubiliers, are those oil/paper?

I had some 220-25 panasonics laying around so I swapped them in for the 25-25 cathode decoupling caps and the amp didn't work. I put the originals back in. Reading Morgan Jones' Valve Amplifiers, I was lead to believe a higher capacitance would only lower the low-filter knee. Whats the deal?

I don't know what speaker load it was designed for, does it even matter if its 8 or 4? If I measure the resistance of the output transformer, will that tell me?

Thanks!
All Things Must Pass


PRR

Re-capping an old tube guitar amp (Riviera 725)
« Reply #1 on: July 24, 2005, 01:19:11 AM »
> believe a higher capacitance would only lower the low-filter knee. Whats the deal?

Should work. Most likely mistake is getting the polarity backward. In the power supply, reversed electrolytics explode. In low level stages they may just un-bias things enough so no signal will pass.

The P-sonic power caps should work fine. I dunno if guitarists find any "magic" in Atoms. It may just be that we have been using Atoms for 30 years, and the P-sonics only got distributed in the US recently.

It won't make a heap of difference what load you put on 6V6. Resistance is not a good clue. On good iron, the DCR might be 5% of the design impedance, but all kinds of strange things are done with guitar amp windings. You could feed 6VAC across the primary, measure the AC at the secondary, and work out the turns ratio.

martthie_08

Re-capping an old tube guitar amp (Riviera 725)
« Reply #2 on: July 24, 2005, 08:32:33 AM »
doesn't look too much like a champ to me, the champ is a single ended amp. I would suggest to install a three prong power cable and if it is noisy, also take a look at the input jacks, if there are dual inputs with shorting jacks.

Gus

Re-capping an old tube guitar amp (Riviera 725)
« Reply #3 on: July 24, 2005, 09:20:40 AM »
There are a number of different champs not all were SE.  There was a small   one kind of like that schematic IIRC.  

Small cap rant with guitar amps.  At 450 to 500 volt rating you do seem to get what you pay for.  There are a few things that seem to have an effect on the life of the cap.  Size, mass and ESR and leakage.

Atoms at that voltage are bigger and also have about 1.5 ohms ESR per 20uf (measured on a sencore lc102)  I have measure some nichicons at a 450V they were fine. Panasonic caps should be fine.

I would not be cheap with cap replacements in the power supply.

When you posted noisy what do you mean hum or hiss...?

Re: Re-capping an old tube guitar amp (Riviera 725)
« Reply #4 on: July 24, 2005, 03:14:56 PM »
Quote from: "Mailliw"
Hi,

I was given this working but very noisy tube guitar amp head. The can-caps on the top are stamped JUL '67. There is basically no info about it on the internet. It was made in Canada.

I drew up the circuit, it is very similar to a Fender Champ, but it has two 12AX7As whereas most champs only have one.

large schematic

small schematic

physical pictures:

top full
top 800x ...
bottom full
bottom 800x ...
bottom right full
bottom right 800x ...
bottom left full
bottom left 800x ...

I read that a lot of people replace 40-450s in Fender amps with spraque atoms, but they are ~5 each bucks at mouser. Would panaonic ecgs be fine? (~2.35 at digikey)

The blue/yellow 0.1uFs are Dubiliers, are those oil/paper?

I had some 220-25 panasonics laying around so I swapped them in for the 25-25 cathode decoupling caps and the amp didn't work. I put the originals back in. Reading Morgan Jones' Valve Amplifiers, I was lead to believe a higher capacitance would only lower the low-filter knee. Whats the deal?

I don't know what speaker load it was designed for, does it even matter if its 8 or 4? If I measure the resistance of the output transformer, will that tell me?

Thanks!




You can use N.O.S Tubes, (GE or Mullard) but not N.O.S ELKOS, and old oil Paper Caps. Vintage but critical:

Not surely in long Time - Elkos (electrolitic capacitors) dry out.  
OIP can fall out/defectively.


Please look www.mundorf.com.
Silver in Oil and Silver with Caps are perfect for the Signalcaps.

M Tube Caps, are High Voltage Tube Caps for the PSU. 3 x 47µf are save and verry fast.

If too few Vintage, then BC Long Live 450 V axially or Panasonic. :grin:

http://www.mundorf.com/english/Capacitors_Amplifier.pdf
http://www.mundorf.com/english/news/news.htm

Dirk T. Jambor
Alles was gut ist, sollte erhalten werden

mcs

Re: Re-capping an old tube guitar amp (Riviera 725)
« Reply #5 on: July 24, 2005, 05:58:20 PM »
Quote from: "MasteringComponents"

Silver in Oil and Silver with Caps are perfect for the Signalcaps.

For an old guitar amp? I would just order the cheap axial ERO caps or something similar...

Best regards,

Mikkel C. Simonsen

Re: Re-capping an old tube guitar amp (Riviera 725)
« Reply #6 on: July 24, 2005, 06:25:24 PM »
Quote from: "mcs"
Quote from: "MasteringComponents"

Silver in Oil and Silver with Caps are perfect for the Signalcaps.

For an old guitar amp? I would just order the cheap axial ERO caps or something similar...

Best regards,

Mikkel C. Simonsen


Yes, you can take a simple old ERO.  
But you give away much sound/sound variety.  
Vov AC30 has silver Mica, and in former times one blocked /used which well and best was for money.  

If you make a Ero, the sound are slowly, but not precise does not have and not warmly, this Sounding.  

If you take ecample one 0.47 µf Silver/Oil an and bypass this with 80 - 120p Mica, you have speed and juicy and flowing, (Color-strong, high-contrast sound), which can let your fingers play easily.  

Feel it simple.  
You take part in silver gold have you purely sound, for very clean and strong tones. :grin:
Alles was gut ist, sollte erhalten werden

Mailliw

Re-capping an old tube guitar amp (Riviera 725)
« Reply #7 on: July 24, 2005, 06:49:14 PM »
Hi,

Thanks for all the info!

Quote from: "Gus"

When you posted noisy what do you mean hum or hiss...?


Its very finicky. When vol/treb/bass are all turned down, it still amplifying a bit. The volume goes up very quickly, 3 is very loud. I'd guess its mostly a hum I am hearing.

When I touch the chassis, a little of the hum goes away. Is that because of the two-prong plug martthie mentioned? The ground connections underneath seemed ok on my multimeter.

The rectifier tube and the two 6v6 tubes are hot enough to burn my finger if I leave it on for more than an instant, is that normal?

Thanks for the help!
All Things Must Pass

Mailliw

Re-capping an old tube guitar amp (Riviera 725)
« Reply #8 on: July 24, 2005, 07:00:39 PM »
I found this post on harmony-central about this amp:

"It has 2 X 6V6, 2 X 12AU7 and GZ34 rectifier tube. It had too much headroom for my taste so I put 2 X 12AX7 and 5Y3 rectifier tube. Now it breaks up around 3 !! This amp is really loud (I use a Marshall cab 4 X 12). However, past 7, it's a mess..."
All Things Must Pass

Re-capping an old tube guitar amp (Riviera 725)
« Reply #9 on: July 24, 2005, 07:11:10 PM »
Quote from: "Mailliw"
Hi,

Thanks for all the info!

Quote from: "Gus"

When you posted noisy what do you mean hum or hiss...?


Its very finicky. When vol/treb/bass are all turned down, it still amplifying a bit. The volume goes up very quickly, 3 is very loud. I'd guess its mostly a hum I am hearing.

When I touch the chassis, a little of the hum goes away. Is that because of the two-prong plug martthie mentioned? The ground connections underneath seemed ok on my multimeter.

The rectifier tube and the two 6v6 tubes are hot enough to burn my finger if I leave it on for more than an instant, is that normal?

Thanks for the help!


You must have all 6V6 tubes perfectly matched.  It humming otherwise.
  You must exchange all ELKO 47µf -200µf for new.  You must test all preliminary stages Tubes.  You must absolutely exchange the rectifier valve.

 
Electro-Harmonix 5U4GBEHThe Electro Harmonix 5U4GBEH is a close replica and an excellent replacement for the classic 5U4GB rectifier tube.
 
TAD-6V6$32.95Price is for a matched pair.  
 
 
 
Tesla (JJ) 6V6SThe new 6V6 from JJ is rock solid and sounds great. Like the EH, it can withstand higher plate voltages making it a great choice in many amps. +++ matched pair +++


Than is the Hum und His from the Amp verry low and ´the sound big
Alles was gut ist, sollte erhalten werden


mcs

Re-capping an old tube guitar amp (Riviera 725)
« Reply #10 on: July 24, 2005, 07:18:17 PM »
Quote from: "Mailliw"
The rectifier tube and the two 6v6 tubes are hot enough to burn my finger if I leave it on for more than an instant, is that normal?

Yes, that's normal. As long as the plates don't glow red (switch off the light to check), you should be OK. But check the caps at the inputs (grids) of the output tubes - if they are leaky the output tubes will die fast...

Just measure the voltage accross the 220k resistors with a high-impedance meter. If the voltage is above 0V the caps are bad.

Best regards,

Mikkel C. Simonsen

martthie_08

Re-capping an old tube guitar amp (Riviera 725)
« Reply #11 on: July 25, 2005, 04:16:26 AM »
Whatever you do to that amp - be carefull, tube amps have voltages / amperes that will kill you if you are not careful!! Always drain the power supply caps with a resistor, because they can still hurt after the amp is turned off.

As Mikkel stated, it is perfectly normal that the tubes get so hot, that you can't touch them.

My suggestion would be to change both power supply caps and coupling caps and cathode bypass caps, then readjust bias and test the amp. Caps will make quite a difference in sound, I once built a 5F1 champ and ended up using Atoms for the power supply, for the high rated coupling caps you can use orange drops, or also mallory 150 (which is what I used).

The GZ34 does give the amp a little more headroom and makes it a little tighter, maybe you can leave it in the amp. I have a fender princeton that was designed for 5Y3, which is running excellent with a GZ34 for the last five years, it is the best sounding amp I have ever owned. But it might be that the GZ34 won't make your specific circuit happy...

CJ

Re-capping an old tube guitar amp (Riviera 725)
« Reply #12 on: July 25, 2005, 02:28:39 PM »
Guitar amps are noisy by nature. But not as noisy as the people using them. most of the time  :razz:

I wouldn't waste a good GZ34 on a Riviera. The good ones (Mullard) go for 100 bucks a pop in some cases, that's more than the amp is worth Now if it were a Rivera amp instead of Riviera, that would be a different story.

5Y3's are fine. You can run into problems when subbing diode tubes - voltages can go hi or lo.

Electrocution? If I hear one more warning on this, I'm gonna puke. Talk to a power line guy. 4160 vac is bad. 200,000 kv is insane. 120 ac? 300 dc? Please cut me some slack. If it were that dangerous, they would not use those voltages for the generaL pubic. I mean public.

If you sub an 8 ohm speak for an old Fender Champ 4 ohm, you will not be a happy camper. In a push-pull, it might not matter.

Here's a maitinanence blurb from our buddy Mr. Pittman:

Disconnect AC line. (doh1)

Bleed the caps(doh2)

Check for loose connections-tighten hardware-move components and wires with a chopstick looking for bad connections

Check for faulty or damaged components- overheating--leaky lytics

Check for arc on tube sockets

Tighten the tube socket pin connections- use a jewler's screwdriver- spary some non lubing contact cleaner in there also

Clean pots-contacts-and switches- spray tuner cleaner into pots and switches, but not pwr or standby

Check bias- make sure speaker is attached

Kick out the jams-mofo!
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Mailliw

Re-capping an old tube guitar amp (Riviera 725)
« Reply #13 on: September 30, 2005, 05:33:06 PM »
Hi,

This one capacitor has a little crack near the lead, and there is no labeling.
Any ideas how big it is?

cap in schem
cap photo

Thanks
All Things Must Pass

VacuumVoodoo

Re-capping an old tube guitar amp (Riviera 725)
« Reply #14 on: September 30, 2005, 05:54:02 PM »
It's an old Philips ceramic cap. In this position it would be between 100-470pF rated at about 100V. The value is color coded, can you read the color bands or are they too faded to see ?
Alex Niemand
_____________________________________
Life's a party but you get invited only once...
Tubewonder amps
"L

Gus

Re-capping an old tube guitar amp (Riviera 725)
« Reply #15 on: September 30, 2005, 06:38:58 PM »
Mailliw

did you install a three wire cord?   The 2 wire cord might be the main cause of the hum.

With caps I think different with guitar amps and effects caps I would not use in a HiFi I might have a good use in a guitar amp( class 3? ceramic at the treble cap)

I would try .022uf mallory 150s for the caps to the output tube .1uf is often to big and this amp does not have a global feedback loop around the output stage.   This helps with open back cabs at loud volumes and small transformers.

 The schematic also looks like you might have the power supply not drawn correctly  You have 4 tubes running off the final node, the PI and the three gain stages maybe the PI goes to the unused node? (Plate, Screen and the unused, right to left)  It looks like it was built to a price point so I would doubt they would waste a cap and resistor.

Some other things to try remove the cap across the cathode resistor of the third stage,  Remove the third stage and add a cathode byass cap[ on the 2nd stage.   Leave like it is but try a 12at7 for the A tube or the B tube I would thing B tube would be better.


Check the taper of the Volume pot most mass produced vol pot are two linear parts at 50% you should get 10% and 90% wiper to ends(R.G.'s site has good info on pots).  The reason I ask is because I heard a rumor that in the 70's some pots were made(for mid fi audio) so turning the gain up a little(10 o clock) would be close to full volume. It was done to trick people into believing the amps were powerful.  Is there any truth to this story I was told many years ago?  I never heard it myself.

the ceramic is a "brighten up" cap

Chris heard a little 6v6 I built that had to much bass with the closed cab were tried it with it has .022uf to the output section it sounds good with the cab I built it with, so sometimes you can adjust caps for the speaker/cab

Mailliw

Re-capping an old tube guitar amp (Riviera 725)
« Reply #16 on: September 30, 2005, 08:11:27 PM »
Quote from: "VacuumVoodoo"
It's an old Philips ceramic cap. In this position it would be between 100-470pF rated at about 100V. The value is color coded, can you read the color bands or are they too faded to see ?


I didn't notice that... nice call. The top portion is brown, then a thick black stripe, then a mustard yellow bottom.

The only ceramic capacitor codes I see are for ceramic disk type, this one isn't a disk, its more of a blob.

If you pretend its a 3 dot ceramic disk capacitor and take the colors from bottom to top (Yellow-Black-Brown), its 400pF. Brown-Black-Yellow is .1uF and nonsense.

400 does fall into your range too... :)

Quote from: "Gus"
Mailliw

did you install a three wire cord? The 2 wire cord might be the main cause of the hum.


Im using 3-wire cord and it isn't making a noticeable difference. I'm just about to place a mouser order for some atom caps and new carbon pots, hopefully its not for nothing.

Quote
The schematic also looks like you might have the power supply not drawn correctly


I think its right, check it out:
open node

Quote
Check the taper of the Volume


Unfortunately I destroyed that volume pot attempting to clean it... a mystery it will remain!

Quote
I would try .022uf mallory 150s for the caps to the output tube


I'll throw some of those mallorys on my order. I'll also give all your other suggestions a try. I will let you know how it turns out.

Thanks for the info.
All Things Must Pass

Mailliw

Re-capping an old tube guitar amp (Riviera 725)
« Reply #17 on: October 30, 2005, 12:21:41 PM »
Hi,

Replaced the electrolytic capacitors, but still got some hum so I am going to replace the big tubes next.

Put my oscilloscope to use for the first time since I got it last week. I use my m-audio soundcard and a tone generator program to put a sine signal into the amp. It puts out a nice clean .2V peak to peak (-27dB on the m-audio mixer) 1kHz sine wave.

If I put the .2Vp-p 1kHz into the amp and turn the amp on full I can hear something in the amp mechanically vibrating at 1kHz. Is that the output transformer making that noise?

Also if I wiggle one of the 12x7a tubes that sits loosely in its socket, I can induce high frequency oscillations, and they are also audible without a speaker. I'm going to replace that socket, but still am curious, how does that happen?

Thank you
All Things Must Pass

jcayer

Re-capping an old tube guitar amp (Riviera 725)
« Reply #18 on: January 26, 2006, 02:49:50 PM »
So did it work ?

Take a look at: http://jcayer2.blogspot.com/

Or http://www.jcayer.com/bricolages/renoamp.htm

Check the subject "Old amp refurbishing"

Thanks  :wink:

Jean
Best Regards,

Jean

Mailliw

Re-capping an old tube guitar amp (Riviera 725)
« Reply #19 on: January 26, 2006, 10:52:31 PM »
I am still working on it :)

Glad you got yours working, good work! Neat that they were made in Montreal.

I'll let you know when I finish.
All Things Must Pass


 

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