How many watts will 2 EL84's do ?

[LevinFan]

Replace the 2 can caps, Antique electronics probably has the right ones or close enough.
Invalid Link Removed
The ones on the underside are paper & foil in wax, they may still be good. Easy to check with a meter, with power on, carefully check for voltage on both sides, on most designs, there should only be voltage on one side, so voltage on both means bad.
It appears to be cathode biased so no neg voltage on the grids of the EL84s.

It doesn’t look like it got much use at all, no discoloring of the resisters or melting of the wax on those caps.

Oh antique also has those odd tubes in case any are bad.

MM

Ok. I'll check 'em out.

So replace the cans first, then check the others ? Also, how do I place the probes ? Black to ground and red to each side ? I've got a multi meter, but I'm new to this stuff, so I have to make sure before I go poking around.

I still need to learn how to make sure caps are discharged and stuff.

 

[LevinFan]

Do I just grab the cans and pull them out, or do I need to make sure they are discharged ?

 

[X Ray]

How many watts will 2 EL84's do ? Ballpark

Ten years ago, I was building low power, rack mount, tube guitar power amps. My design used a two EL84 A/B output stage and did just over 10 watts. I forgot what plate voltage I was running. I think 380............I can't remember.

Turned all the way up, through a 4x12 with some Vintage 30's, they sound SWEET.

 

[Red Planet]

Just for kicks.

You can squeeze 50 watts out of four EL84's. The Tubes must be JJ, any other EL84 can not do it.

One must limit the amount of Voltage the Grid can get or the Grid will disintegrate.

 

[MAMMOTHvolume]

Do I just grab the cans and pull them out, or do I need to make sure they are discharged ?

take it to a tech to do it for you, if you want to learn ask if you can sit in.

 

[LevinFan]

take it to a tech to do it for you, if you want to learn ask if you can sit in.

That may be best.


EDIT: I just realized caps have to be formed. I'll just take the two chassis to a tech and let them work some magic.

 

[johnk_10]

That may be best.


EDIT: I just realized caps have to be formed. I'll just take the two chassis to a tech and let them work some magic.

they often don't have to be formed, but i always do it anyway. if you're asking whether you should discharge them or not, you should take it to a tech, however, if the amp hasn't been turned on in years, i doubt that there's any charge left in them. (but better safe than sorry!).

PS. some techs will tell you to put in higher uf values (more filtering), but i wouldn't recommend that. i'd just replace them with the same uf values (but ones with higher voltage ratings wouldn't hurt).

 

[LevinFan]

they often don't have to be formed, but i always do it anyway. if you're asking whether you should discharge them or not, you should take it to a tech, however, if the amp hasn't been turned on in years, i doubt that there's any charge left in them. (but better safe than sorry!).

PS. some techs will tell you to put in higher uf values (more filtering), but i wouldn't recommend that. i'd just replace them with the same uf values (but ones with higher voltage ratings wouldn't hurt).

Ok, noted. I didn't ask if it had been used recently. It came out of an estate sale, and the power cord was tukced inside with a ton of dust on it. I didn't power it up because of that, and from what I understand, sitting idle for a long time will make caps go bad.

Here are some suggestions I got on another forum

OK...so this old beast has a stereo power amp with two open ended EL84 (6BQ5) amplifiers powered from a common power transformer. Here is what I would do. I would use the power transformer and reconfigure the two EL84s and a couple of 12AX7s to build an 18 watt Marshall clone or a VOX AC15. Probably a Lite IIb or such. You would have to buy or scrounge an appropriate output transformer since the two that are there are too small for a push/pull 18 watt amp. With a little luck and skill you can probably reuse the chassis. I would recommend using new ceramic tube sockets (although it's up to you), pots, jacks and components. Using a turrent or eyelet board would also be advisable. Still, you have the basis of a nice inexpensive little screamer here. Before you start check out what the B+ is. Keep in mind that it will be a little higher if you use an SS rectifier to free up heater current for another 12AX7.

One of the 'top' pics makes the RCA look like it has a quad of 6BQ5s, so I think you have a stereo pair of 10-15W power amps there, and enough heater current to run 2 phase inverters and 2 more preamp tubes - look them up and note their heater currents - 12AX7s running on 6.3VAC want 300mA per tube.

Remembering that I'm a feature creep, I'd probably do something like a Fender Blackface preamp - the vibe channel of an AB763 deluxe - or something like a Vox AC30TB preamp - and then run an FX loop with a stereo return.

I'll just find a tech and let him do it. I'll pull the preamp chassis and hopefully, it can be used and modded as well.

 

[bassmodder]

You are usually up sh%^ creek if you want to use the built in EQ and preamp from one of those if it was only a record changer. More than likely it will have an RIAA curve built in (for the records) and will sound funky with guitar.

I have tried this and sometimes you can EQ it out but more often than not it just does not sound right.

I would really use that amp for hi-fi as it is a stereo amp and they are quite desirable. Just check the bay! You might be able to trade it for something more sutable like an old PA head which will suit your needs much better and have money left over.

With a stereo amp- do onto one as the other. You have 2 amps in one chassis. Twice the work, twice the cost. Some old Bogen PA heads fetch around 50 bucks and will use either 6l6 or 7868 tubes for about 50 -100 watts. Also keep your eyes on some of the old Dukane school PAs. You can convert the 8417 tubes to 6550 with minimal work.

Just saying do some research before you trip that over to a tech for an overhaul.

Or... get it restored and open your ears to what Hi-fi stereo should really sound like... That victor is a nice phonograph with a new stylus. Yours is in collectors condition as well.

 

[bassmodder]

they often don't have to be formed, but i always do it anyway. if you're asking whether you should discharge them or not, you should take it to a tech, however, if the amp hasn't been turned on in years, i doubt that there's any charge left in them. (but better safe than sorry!).

PS. some techs will tell you to put in higher uf values (more filtering), but i wouldn't recommend that. i'd just replace them with the same uf values (but ones with higher voltage ratings wouldn't hurt).

There are advantages. I do this in my Hi-fi amps for cleaner sound and more oomph. My dynaco will arc and destroy the rectifier tube if it does not cool all the way down before being switched back on. Of course I added all the extra capacitance after the choke and the first section is at the datasheet maximum for the tube.

The result: I can just about lay it to the floor and the bass will stay clean. Even the kick drum. Wide open, the amp has an even distortion across the lows and mids. Sounds pretty cool actually and is so loud that I can not stand in front of it comfortably.

 

[LevinFan]

You are usually up sh%^ creek if you want to use the built in EQ and preamp from one of those if it was only a record changer. More than likely it will have an RIAA curve built in (for the records) and will sound funky with guitar.

I have tried this and sometimes you can EQ it out but more often than not it just does not sound right.

I would really use that amp for hi-fi as it is a stereo amp and they are quite desirable. Just check the bay! You might be able to trade it for something more sutable like an old PA head which will suit your needs much better and have money left over.

With a stereo amp- do onto one as the other. You have 2 amps in one chassis. Twice the work, twice the cost. Some old Bogen PA heads fetch around 50 bucks and will use either 6l6 or 7868 tubes for about 50 -100 watts. Also keep your eyes on some of the old Dukane school PAs. You can convert the 8417 tubes to 6550 with minimal work.

Just saying do some research before you trip that over to a tech for an overhaul.

Or... get it restored and open your ears to what Hi-fi stereo should really sound like... That victor is a nice phonograph with a new stylus. Yours is in collectors condition as well.

Great info. Yes it is gorgeous. I thought it had 10's in it, but they are RCA 12". I haven't checked the impedance yet. It also has 4 smaller speakers, I haven't looked at yet.

It hasn't been used for quite awhile I'm guessing. I pulled the preamp chassis. It's roughly 12" x 2 3/4" x 2 ". The caps look pretty nasty, and all the wiring between the two chassis and the turntable is nasty and sticky.

It's a really cool piece of Americana for sure. The legs are off in the pic but I have them.

I'll look and see what they sell for in working condition, and weight the options. I'd love to have it for my old albums, but it's too big to keep. I may let it simmer. That power amp chassis has tons of room though, for adding a tube preamp and a good output transformer.

I'd rather it wind up with someone who will love it for what it is, but unless I can sell it or trade for a point to point amp, I'll try and sell what's left to help fund the mods.

I dunno, I'll might throw it on the classifieds here. Someone may have an amp to trade.

 

[ashtray]

FWIW - I used to have a Seymour Duncan guitar amp, rated at 50 watts, using a quartet of EL84's. (can't recall the model name, but they made a cheaper import version that was only rated at 40 watts with the same tube config).

I think I've seen a pair of EL84's do 30 watts in a guitar head recently (Egnator?) - but never heard of more than that. For higher powered stuff, people use the EL34's, which do 25 watts each easily.

 

[LevinFan]

they often don't have to be formed, but i always do it anyway. if you're asking whether you should discharge them or not, you should take it to a tech, however, if the amp hasn't been turned on in years, i doubt that there's any charge left in them. (but better safe than sorry!).

PS. some techs will tell you to put in higher uf values (more filtering), but i wouldn't recommend that. i'd just replace them with the same uf values (but ones with higher voltage ratings wouldn't hurt).

I've been informed that the cans are pricey, and it may be best to discard them and use separate caps underneath.

Anyhow, I happened on a good article on EL84's and I want a Vox-like amp with them pretty bad.

 

[LevinFan]

FWIW - I used to have a Seymour Duncan guitar amp, rated at 50 watts, using a quartet of EL84's. (can't recall the model name, but they made a cheaper import version that was only rated at 40 watts with the same tube config).

I think I've seen a pair of EL84's do 30 watts in a guitar head recently (Egnator?) - but never heard of more than that. For higher powered stuff, people use the EL34's, which do 25 watts each easily.

yea, my old Sano has a pair of EL34's. It originally had 8417's. A tech looked at it and said they modded it right. It does roar in a good way.

I want to run two amps with my strats and I bought an old '76 Randall RG-120-410 combo cheap off cl. 120 watts and weighs a ton. Sounds great set clean with the Sano dirty, but I'll probably flip it to help fund the mods and a cab for this RCA. And save my back while I'm at it.

 

[MAMMOTHvolume]

they often don't have to be formed, but i always do it anyway. if you're asking whether you should discharge them or not, you should take it to a tech, however, if the amp hasn't been turned on in years, i doubt that there's any charge left in them. (but better safe than sorry!).

PS. some techs will tell you to put in higher uf values (more filtering), but i wouldn't recommend that. i'd just replace them with the same uf values (but ones with higher voltage ratings wouldn't hurt).

whats your reasoning behind this? i always recommend bigger caps when it comes to bass aslong the PT / rectifier can handle it. It means theres less sag and thus more low end and smoother distortion when cranked

 

[johnk_10]

whats your reasoning behind this? i always recommend bigger caps when it comes to bass aslong the PT / rectifier can handle it. It means theres less sag and thus more low end and smoother distortion when cranked

Higher uf value caps always make tube amps sound more harsh, stiff and brittle. i have repaired/serviced/restored thousands of vintage tube musical instrument amps in the last 35 years, and this has ALWAYS been the case. There is definitely NOT more low end (actually less!). Electronic engineers seem to always think its better to put in higher values, because in theory, it provides cleaner power, and in solid state amps, it can benefit them, but not in vintage tube amps. Ask any tube amp repairman or boutique amp builder that has alot of experience and you'll find that they agree with me.

an excellent example is the Fender Tone Master amp. I have modified more than 50 of them by replacing their 220 uf primary main filter caps (wired in series to get 110uf) with 80uf caps (also wired in series to get 40 uf) to make them sound alot more like vintage blonde Fender amps from the early '60's. every customer, from novice to expert was thrilled with the results, giving the amp more low end, depth, and compression, rather than having them 'bark' at you in their stock form. it is very surprising how good those amps really are, but only after the mod.

the reissue '59 bassman is also another excellent example. they don't sound anything like the originals, and its not just due to the vintage speakers or USA tubes. their power supply filtering is very different. the input caps on the original Bassman has two 20uf in parallel for 40uf total, whereas the reissue has two 100uf in series for 50uf total (not a big difference, but NOT the same). there's also extra capacitance on the filter output stage. the original Bassman had a single 8uf cap whereas the reissue has two 22uf caps in parallel for a total of 44uf (huge difference!). some techs just clip out one of the 22uf caps to get it closer to the original, but i always replaced them to the stock values or at the very least, rewire them to series to get 11uf.

i wish i had a nickel for how many times my customers complained that after having a previous tech go thru their amp, replacing their filter caps with higher uf values, that their amp was never the same and sounded harsh so they stopped using it. i always told them, bring it in and i'll put it back to the way it was when you loved it. it never failed.

back in the day, the CBS 'engineers' at Fender also thought the higher uf value caps were better, as do the current amp 'designers' at Fender now. Sorry, but to me they are idiots and have no business 'redesigning' amps and calling them 'true' reissues. Leo Fender was a friend of mine, and he told me that when an electronics engineer told him to put higher uf value caps in his amps to make them 'cleaner', his response was " They don't need it, because most musician's have distortion in their lives."

 

[Passinwind]

Higher uf value caps always make tube amps sound more harsh, stiff and brittle. i have repaired/serviced/restored thousands of vintage tube musical instrument amps in the last 35 years, and this has ALWAYS been the case. There is definitely NOT more low end (actually less!). Electronic engineers seem to always think its better to put in higher values, because in theory, it provides cleaner power, and in solid state amps, it can benefit them, but not in vintage tube amps. Ask any tube amp repairman or boutique amp builder that has alot of experience and you'll find that they agree with me.

+1

I can think of a few exceptions to this though -- mostly in off-brands where the original values were underspec'ed a little too much, or when various mods require a little more filtering for stability or noise issues. At which point, it's not really a vintage amp anyhow...

 

[BassmanPaul]

Great post John and accurate in its conclusions. Another point about the main filter cap is that if the amp has tube rectification you have to stay within the tubes ratings. A 5AR4, for instance, has a maximum of 30µF specified in its specifications. I've seen 100µF used as a replacement. The owner complained that the amp kept blowing rectifiers. Dropped it to 20µF and the problem went away.

Paul

 

[BassmanPaul]

I've been informed that the cans are pricey, and it may be best to discard them and use separate caps underneath.

Anyhow, I happened on a good article on EL84's and I want a Vox-like amp with them pretty bad.

They can be pricey yes but so can separate caps.

If you want a VOX like amp you would need a bigger power transformer AND output transformers. The AC15 and AC30 are closer to Class A than AB so you would have to factor the increased quiescent current.

Antique Electronics has transformers available and the multi caps.

I would leave the amp you have basically alone and start fresh. There are not too many useful parts in the existing amp.

Paul

 

[LevinFan]

They can be pricey yes but so can separate caps.

If you want a VOX like amp you would need a bigger power transformer AND output transformers. The AC15 and AC30 are closer to Class A than AB so you would have to factor the increased quiescent current.

Antique Electronics has transformers available and the multi caps.

I would leave the amp you have basically alone and start fresh. There are not too many useful parts in the existing amp.

Paul

I had a link to the schematic, but now it won't work, and I didn't save it while I was there. But the pt is a pretty big one and if I was reading the schematic right it was sending 350 volts.

here is the schematic link... cool site too

Link Removed