My first build: Ceriatone 36W EF86-questions!

[RockinDoc]

Hello to all,

I have been lurking here for a while, and I'm impressed by all the knowledge and expertise here.

I've am just finishing my first build and would appreciate any help prior to firing it up. My previous electronic/soldering experience consists of dropping a set of Lindy Fralin pickups into my Strat - a messy job, but they sound great. (I know, I know, the 36W EF was probably not the best choice for a first build, but I realized that AFTER I received the kit!)

I'll try to upload some pix, which will reveal that the secondaries have been desoldered; I had planned to follow the advise of a certain Paul Ruby who suggests checking continuity first, then checking the low voltage 5V and 6.3V circuits, and then the HT secondary (how ever the best way is to DO that).

I should add that I have read everything I could find on the web regarding electrical safety, grounding, discharging capacitors, me as a low resistance path, fibrillation vs 4th degree burns, etc, etc. I have a couple of 5 watt, 10K resistors to make a discharge tool (is that about right, or more resitance?), and I THINK I'm appropriately paranoid about shockage.

Anyway, my options are to ask my questions here and reveal my abject ignorance for all to see, or is there anyone here willing to PM me with an email addy or whatever to preserve some degree of dignity for me?

Thanks in advance, and I'll try getting pictures on when I have more time (or should I make a gallery, or is that only for proven veterans?)

[Phil_S]

Like most newbies, you will need to flap in the breeze with your errors. We all make them at first. For example, I build an amp that didn't work right because I put in 1M plate load resistors instead of 100K. I didn't read the stripes properly and kept thinking that wasn't the problem. The advantage of posting to a forum is that you will gain from the collective wisdom. I'd encourage you not to feel bashful. Rather, the only silly question is the one you didn't ask. Besides, this stuff can be dangerous and the group-think will also tend to spot safety problems more quickly.

For your discharge tool, a pair of 'gator clips, wire, heatshrink and that 5W 10K will work fine in most cases. Mine is a 10W model. You can probably use a 1K resistor just as effectively.

[RockinDoc]

Hello again and thanks for the previous responses,

I finished my 36W EF 86 about 4 or 5 days ago, went through the anxiety of first start-up, and have been playing it, and it does indeed sound very nice (not to mention louder than hell!) It was pretty fierce through my old Tremolux's 2X10, but through my Avatar 2X12 with one greeenback and one G12H it is downright apocalyptic!(even on "low" power, ie 18 watts).

I did want your input on my voltages in terms of maxing out the EL84s and also the voltages in the EF 86, which is the front-end for the "Vox/Matchless" channel.
Please bear in mind that this is my first build and first real foray into electronics, other than putting replacement PU's in my Stratocaster...so don't assume that I know much of anything, although I have read enough to build the amp and not get shocked or worse.
Nik at Ceriatone has been very helpful in fielding specific questions, but they send out their kits with no instructions whatever, so I had all the components and only the layout I printed off their website (and a LOT of info off the web, largely from this fine site).

OK, voltages:

Heater and rectifier low voltage readings all right on.

Initial readings B+ 350V, first stage cap 283V, second stage cap 262V, power stage cap 288V. I am not sure about this, but the very first DC coming off the GZ34 I am calling B+.
The caps above are the large electrolytics that serve each stage. Is this at all close to a correct classification?

EL84's: Plates 365V; grids (screen?) 350V (this is on "low" power, it has a half power switch. The plate/grid voltages were lower on high power, ie, 340/319V); is this correct, or do I have it wired in reverse? Cathodes all equal and consistent.

The 3 12AX7's, including the PI, all seem within where one might expect them, and they are consistent whether on full or half power.

The EF 86 concerns me in that the plate readings are 96/88V, again low/high power switched, grid is 112/102V. Cathode 2.2V.
I had looked up the specs on this tube and they mentioned 300V max on plates, 200V on grid (!!)

At any rate, I was wondering:
1) am I over the top with the power tube voltages? (I read lower voltages for maxes on the maker's spec sheets; nothing is running hot that I can see, no red-plating after 30 to 60 minutes of powering up or playing time, PT just warm). I like the way it sounds, great power tube saturation, but I don't want to shorten their lives TOO much, or worse.

2) Any ideas on the readings on the EF 86? Seems hard to find a whole lot of info out there on running these. I worry that if this is way too low, then I could be getting better tone from this channel.

3) Have I gotten something screwed up with the half-power switch? The voltages are higher with the switch thrown to low power, which should be roughly 18 watts vs 36 (and vice versa). I followed the layout to a "T", and Nik hasn't had a chance to get back with me yet.

Thanks so much for any and all feedback.

[RockinDoc]

bump

[tarzanalog]

My amp (same as yours) is out on loan to a studio right now or I'd have posted my voltages for you for comparison. I'll post as soon as I can.

It makes sense to me that the voltages would be slightly lower when running all four tubes... they're sharing the same PT and the load would be greater. I AM surprised that the grid voltage dropped 31V though. That's pretty significant. Gotta get mine measured and post!

The EF86 voltages ARE surprising. (Shame on me... After my build I doubled checked my wiring, measured voltages on the output tubes, and fired it up! I never thought to check the preamp voltages... it sounded so good.)

I'll demand my amp back today and get those checked.

Thanks for your posts!

[RockinDoc]

Tarzanalog,

Hi man, appreciate the response. Is yours from scratch or a kit? Do you get any moderate hum above about MV 4-5, gain 6 or so on the 12AX7 cannel? (less with humbuckers)

Anyway, I finally got a response from Nik's guys at Ceriatone, and the voltages ARE lower on full power, higher on half power. Same with their Matchless DC-30 clone (EL84's).

Still, even the Matchless' voltages on low power are around 340's plate/grid, whereas mine run about 365/350! They don't appear to be too hot (can you tell by looking for red-plating or something?)

The 36W EF voltages they gave me were around 313 on full power, which tells me mine are running a good bit hotter.

Also, it looks like my EF 86 voltages that looked so far below the published max's are in the same territory as what their 36W is, and their DC-30 runs a little bit higher than mine on Plate, lower on grid. Can't explain that though. Any ideas?


One other puzzler for me is this: their power tube numbers on half power show that the cathode voltages on the outside PP pair are roughly doubled. How does that work to cut the power in half?

I know this is a lot of stuff to ask, but if you or any other of these strong, silent types out there have any ideas, I'm all ears

Thanks in advance.

[Holmes]

RDoc,

Sorry, don't stop by here often but noticed your recent posts.

I have a scratch built 36TMB + EF86 based on the C'Tone layout for same. I used Weber transformers so I will get somewhat different voltages than you do but will try to answer questions to the limits of my rather dubious technical understanding.

Full power will show lower voltages than half power because the load on the power supply is larger and rectifier will sag a little more and all power resistors in the power supply will show higher voltage drops. Most of the load without an input signal is the EL84 idle power.

You need to calculate plate dissipation on your EL84s to ensure that you are running at safe levels. I am currently running just a shade over 10 watts per tube. If you search this forum you will find guidance in doing this. If you need help let me know and when I have more time will go through it.

Your EF86 voltages look fine to me. They run fairly low compared with maximums for the tube in this design.

EL84 cathode resistor voltage drop should be similar for 1/2 or full power. There must be an error or nomenclature confusion in the data you are looking at. I get about 12 volt drop for 2 EL84s and about 10 volt drop for qty 4 EL84s. You will need to tailor your cathode resistors to get the proper idle dissipation. I am running 75 ohms (10 watt rating) on full power and 157 ohm (10 watt rating) 1/2 power but my plate voltage on EL84s is 325 VDC.

I have attached an Excel spreadsheet which shows my voltages and calculated plate and screen dissipation (use at your own risk) for my 36W.

Hope this helps,

Holmes

[tarzanalog]

Is yours from scratch or a kit?

Ceriatone Kit. Ceriatone Iron. JJ GZ34 and EL84s, Phillips 5751 PI, Tung Sol RI ECC803S and 12AX7, and Amperex 6267.

Do you get any moderate hum above about MV 4-5, gain 6 or so on the 12AX7 cannel? (less with humbuckers)

Noise floor goes up pretty quick on TMB channel with MV and Volume both past 8... otherwise it's pretty quiet.

They don't appear to be too hot (can you tell by looking for red-plating or something?)

You'd be able to see the red-plating. It's just that... the plates glow from the center out and the red usually goes away when you play a series of notes. FWIW - I've seen EL84s in AC30s that were very unhappy and then JJs in the same amp and they were fine. I have a set of Sylvania blackplate 6BQ5s that sound super sweet in my 36W but have less output vs. the JJs. I use those for recording ($125 matched quad) and the JJs for everyday use.

What's your wall AC voltage? A few volts off spec there can dramatically affect your voltages in the amp.

[gene]

Just an "oh, by the way." If the half-power switch removes a pair of the EL84's from the circuit by disconnecting the cathodes only, you would see the full B+ at their plates as the tubes are not conducting. Unfortunately I am not familiar with the circuit, so take this with a grain of salt.

gene

[RockinDoc]

RDoc,


You need to calculate plate dissipation on your EL84s to ensure that you are running at safe levels. I am currently running just a shade over 10 watts per tube. If you search this forum you will find guidance in doing this. If you need help let me know and when I have more time will go through it.

Your EF86 voltages look fine to me. They run fairly low compared with maximums for the tube in this design.

EL84 cathode resistor voltage drop should be similar for 1/2 or full power. There must be an error or nomenclature confusion in the data you are looking at. I get about 12 volt drop for 2 EL84s and about 10 volt drop for qty 4 EL84s. You will need to tailor your cathode resistors to get the proper idle dissipation. I am running 75 ohms (10 watt rating) on full power and 157 ohm (10 watt rating) 1/2 power but my plate voltage on EL84s is 325 VDC.

I have attached an Excel spreadsheet which shows my voltages and calculated plate and screen dissipation (use at your own risk) for my 36W.

Hope this helps,

Holmes

Holmes,

Very helpful, thanks. I notice your PT secondary is, what, 340V? Mine's 290, if that means anything.

I have not calculated plate dissipation. I know the formula but don't really know how to put it into play, and, this may sound dim, but I have never measured current. Any advice would be appreciated. I have read that up to 12 watts is fine with EL84's.

As far as the half power cathode voltages, Nik's guys sent me voltages that showed roughly half the voltage on the inner pair! Don't know what that means but I recall getting something similar. I'l check when I get home.

your speadsheet is very thorough. Thanks, I will try to use it wisely

[RockinDoc]

Is yours from scratch or a kit?

Ceriatone Kit. Ceriatone Iron. JJ GZ34 and EL84s, Phillips 5751 PI, Tung Sol RI ECC803S and 12AX7, and Amperex 6267.


What's your wall AC voltage? A few volts off spec there can dramatically affect your voltages in the amp.

Tarzanalog,

Thanks for the input. The 6267 is an EF86 equivalent? Same microphonic tendencies?

Don't know my wall voltage; I assumed it was about 120V. In fact, now that I think about it, I remember checking at the mains on the amp when I was beginning all my voltage checks (those first few nailbiting minutes) and I believe it was reading about 122-123V. Would that be enough to have a significant effect? If so, what to do?

[RockinDoc]

Just an "oh, by the way." If the half-power switch removes a pair of the EL84's from the circuit by disconnecting the cathodes only, you would see the full B+ at their plates as the tubes are not conducting. Unfortunately I am not familiar with the circuit, so take this with a grain of salt.

gene

Gene,

Not sure on that one. When I checked the voltage on full power, cathodes on the EL's were all 11 or so, all the same. On half power, the inner pair weredown, and I can't remember exactly by how much (I'm at work), but it seems like it was roughly by half. Would that qualify as disconnecting them? (I noticed the same thing on test voltages Nik sent me on a DC-30 clone, cathode voltage difference on half power).
Thanks for the input.

[tarzanalog]

... The 6267 is an EF86 equivalent? Same microphonic tendencies?

Don't know my wall voltage; I assumed it was about 120V. In fact, now that I think about it, I remember checking at the mains on the amp when I was beginning all my voltage checks (those first few nailbiting minutes) and I believe it was reading about 122-123V. Would that be enough to have a significant effect? If so, what to do?

I've had better luck buying the EF86 military equivalent 6267. Less prone to uPhonics in my experience.

My normal wall voltage is 117V. So, assuming roughly a 1:2.75 PT windings ratio... where I'm getting around 321.75V you'd be getting around 338.25. That's only a 16.5V swing I know, but still something to consider.

[RockinDoc]

Thanks.

BTW, does microphonics manifest as squeal, hiss/hum, or picking up AM radio stations such as occurred with me while testing voltages on my EF86? Or something else entirely?
Do these 6267 tubes have about the same characteristics as the EF86? Are they available as NOS, or mostly new prod?

I am planning to check my plate dissipation on these EL84's; if anyone has any guidance, let 'er rip! I have seen the formula, but am not sure about measuring current, etc. I'm about to search for this, but who knows?

[Holmes]

RDoc,

OK here goes.

With the amp on, off standby, all pots at zero with no inputs connected and speaker connected....

Measure voltage drop across your power tube cathode resistor. The cathode resistance will be denoted Rk. In full power mode (4-EL84s) this will be one of the cathode resistors (the one with an end grounded directly to the ground buss, shown as a 68 ohm resistor on the layout I have). In half power position you will be measuring voltage drop across both power tube cathode resistors (68 + 62 ohm). The voltage drop across the cathode resistor will be denoted Vk.

Measure voltage between pin 7 on your EL84s and ground for each tube. You may see a slight difference between the "push" vs "pull" tubes (pink vs grey or whatever colors are used on the OT primary leads). This we will call Vp.

Next we will measure the screen resistor voltage drop. Measure voltage drop across only the 82 ohm resistor connected to power supply point A and pin 9 of each EL84. Call this Vsd. Calculate screen current as Is = Vsd/82 (use the value for the screen resistor if it has changed from the 82 ohm value, this screen current is usually about 0.003 A or 3 milliamps).

We are finally ready to do some work here.

Calculate cathode current Ik, for 4 EL84 tubes it is:
Ik = Vk / (4 * Rk)
typically about 0.036A or 36 milliamps

For 2 EL84 tubes it is
Ik = Vk / (2 *Rk)
about 38 milliamps

The idle dissipation for each EL84 power tube is
P = (Vp - Vk) * (Ik - Is)

Example
P = (325 - 10.7) * (0.036 - 0.003) = 10.3 watts

Hope this helps.

Others please correct me if you see any errors.

As far as microphonics on the EF86 they come in many forms from ringing, trailing metallic tones and even raspy sounds. Good EF86 tubes are hard to come by. I am leaning towards finding substitute tubes.

Kindest,

Holmes

[Holmes]

RDoc - In case you are interested this is my current schematic.

Holmes

[RockinDoc]

Holmes,

Many thanks for this. All based on V=IR, right? The part that had me baffled, I guess, was how to integrate the fact of different numbers of power tubes, the PP configuration, and full vs half power. So thanks again.

I'm going to test this tomorrow at home and report back.

BTW, could microphonics manifest as a metallic ringing (brief) when flipping toggle switches, like standby, half power, etc?

[tarzanalog]

Once a tube goes microphonic it's more prone to picking up mechanical vibrations like that. Making EF86 tubes less than ideal for use in combos with their increased vibration from the speaker(s). If it's so bad that it's picking up its own internal vibrations then it can self oscilate and squeal.

FWIW, I found a sleeve (5) of these NOS 6267s locally for $50. They're the Amperex Orange Globe branded tubes and so far all are very quiet and very strong. I also have several Sylvania branded 6267s that are also very good. I've had a pretty good experience with the RI Tung Sol EF806... maybe I've just been lucky?!? I've also read in various places that the EH EF86 is just as "good" as the TS, but while the EH tube that came with my Ceriatone was not uPhonic... it was a little on the dull side. Regardless of what tube is in the floating socket, the silicone rings help immensely in keeping them quiet.

[RockinDoc]

RDoc - In case you are interested this is my current schematic.

Holmes

Holmes, very helpful as well. Just getting OK w/ reading schematics, and I can see the similarities and differences in our amps.

Questions, if you don't mind:

What is the alternate V1 you have and what's that for? Different tone mostly?

Do you ever use NFB?

The top cut, is that like on the old AC-30's? How do you use that?

Do you have to mod the amp to use a reverb unit (free standing)

thanks again,