Alternative Power Tubes for APPJ EL34 + 6N4

[GuyNoir]

Hi there:

I purchased an APPJ El34 + 6N4 (no model number)

It came with EH EL34s. I've tried EH fat bottle 6AC7s, and most recently JJ KT77s. I thought the fat bottles were marginally better than the EL34s, but both perhaps a bit polite as the midrange from my ADS L810 is slightly recessed. The JJ KT77's opened up the midrange some, but they are somewhat brash. That's with rolling Genelax 12AX7 and triple mica 5 star GE 5751.

The amp is advertised as being compatible with el34, 6ac7, and kt77, with practically no literature available. Does anyone know if KT66, KT88, etc.might an option? "Self Biasing" if that means anything. Also,I'm searching for a kt77 that might be a bit more refined than the JJ. Any opinions or recommendations appreciated!

 

[CZ4A]

I think there might be a typo in the compatible tube list. 6AC7 should be 6CA7, which is simply the US designation of the EL34. The 6AC7 is an older tube with a different pin-out and lower max ratings.

I have the APPJ PA1502A headphone amplifier (12AX7 + 2x 6V6). I can get you the e-mail address of the distributor later tonight. Their English is iffy but they were helpful with providing ratings for my amp, which helped a lot with rolling.

I'd be interested to see one of these EL34 amps opened up. APPJ shared the same basic circuit of the PA1502A with a couple of its other amps (12AX7 + 2x EL84 speaker amp, 2x Compactron speaker amp). If the EL34 and PA1502 are similar then the preamp tube runs off of 12V instead of 6V. Not a big deal if you stick to 12AX7 family tubes, but it will affect your choices if you decide to get adventurous like I did.

 

[GregBilodeau]

My favorite tube in this family is the new Gold Lion KT77. I use them in a TVA10 and have tried a number of others and always go back to the Gold Lions.

GregB

 

[GuyNoir]

I think there might be a typo in the compatible tube list. 6AC7 should be 6CA7, which is simply the US designation of the EL34. The 6AC7 is an older tube with a different pin-out and lower max ratings.

That was a typo on my part.

I'd be interested to see one of these EL34 amps opened up. APPJ shared the same basic circuit of the PA1502A with a couple of its other amps (12AX7 + 2x EL84 speaker amp, 2x Compactron speaker amp). If the EL34 and PA1502 are similar then the preamp tube runs off of 12V instead of 6V. Not a big deal if you stick to 12AX7 family tubes, but it will affect your choices if you decide to get adventurous like I did.

I'm reasonably sure the internals of this one are essentially the same as the EL84/12AX7 amp, which I owned at one point. I had the bottom off to repair it, as one of the feet and associated corners was crushed in. It's obvious that it has a switching power supply. It's dead quiet; no hiss nor hum with my 93db efficient speakers. Other than that, it's very top heavy and I know the output xformers are of high quality. I figure 8 wpc should give me 103db of output in near field, and it's not hard to believe. Very room filling and astonishing loudness with no perceived distortion. I know the the Musical Paradise mp-301 will take virtually anything in the KT family, so I figured this one might as well. I'm wondering about a KT66, which I've read excel at midrange.

My favorite tube in this family is the new Gold Lion KT77. I use them in a TVA10 and have tried a number of others and always go back to the Gold Lions.

GregB

I've an itchy trigger finger for the Gold Lions! I have to say the JJs are very good for the price. In fact, I have a generic, late looking GE 12ax7 that I just put in that really balanced out the perceived edginess of the JJs.

Thanks Gents.

 

[primosounds]

The 6L6 family of tubes can be used except the metal covered 6l6. I find that the vintage 6l6g sound better in my SE amp than el34 tubes. Even metal 6l6 sound great but you can't use that one since the shield or the metal cover of the 6l6 is on pin 1 which is connected G3 on the el34. IME, on Altec 19 speakers, with my custom made SE amp with Transcendar Output trannys, the Mullard EL37 has the most precise, cleanest sound.

 

[Tim64]

I'd be interested to see one of these EL34 amps opened up.

Here is a picture I found of the circuit board and switching power supply.

 

[GuyNoir]

The 6L6 family of tubes can be used except the metal covered 6l6. I find that the vintage 6l6g sound better in my SE amp than el34 tubes. Even metal 6l6 sound great but you can't use that one since the shield or the metal cover of the 6l6 is on pin 1 which is connected G3 on the el34. IME, on Altec 19 speakers, with my custom made SE amp with Transcendar Output trannys, the Mullard EL37 has the most precise, cleanest sound.

Oh I love the look of those 6L6g! Same pinout as an EL34, eh? My goodness, the EL37 command a premium! They're gorgeous as well. Thanks for the advice.

 

[CZ4A]

That was a typo on my part.

No worries. I saw the same typo in the Massdrop and Amazon listings!

I PM'd you the e-mail address. If you get the max ratings from the distributor, please share them here.

If you're looking for NOS 6L6s on a budget, I recommend the 6BG6G with 6L6 adapters. The 6BG6G is the same tube as the 6L6G, except with a top cap and different pin-out for use in TV sets. Even with the necessary adapters, you could get them for cheaper than a pair of vintage 6L6Gs with a little shopping. I bought the adapters as DIY kit from http://www.vacuumtubes.com/6BG6.html, and there are prebuilt adapters available from eBay.

I'm using Tung-Sol 6BG6Gs in my amp, shown here with a Telefunken ECC803S preamp tube. The biasing in the APPJ works quite well, at least for the preamp tube- my ECC803S is extremely weak, to the point I can't bias it in one of my other amps, but it works fine (and sounds stellar!) here.

Here is a picture I found of the circuit board and switching power supply.
View attachment 1153572

At a glance, that looks an awful lot like the PA1502A's board, down to the grey coupling caps and Nichicon cathode bypass caps. I've replaced those caps in my amp and the improvement in, well, everything, was crazy! There's a future upgrade if OP gets bored with tube rolling.

 

[Tim64]

At a glance, that looks an awful lot like the PA1502A's board, down to the grey coupling caps and Nichicon cathode bypass caps. I've replaced those caps in my amp and the improvement in, well, everything, was crazy! There's a future upgrade if OP gets bored with tube rolling.

I have the APPJ PA0901A using 6bq5's and was thinking about doing a capacitor upgrade. Is the board up to snuff to de-soldering without self destructing?

 

[GuyNoir]

I have the APPJ PA0901A using 6bq5's and was thinking about doing a capacitor upgrade. Is the board up to snuff to de-soldering without self destructing?

Do you feel lucky? It looks pretty delicate to me, though I'm sure a deft and experienced hand will prevail. That rules me out.

 

[GuyNoir]

No worries. I saw the same typo in the Massdrop and Amazon listings!

I PM'd you the e-mail address. If you get the max ratings from the distributor, please share them here.

If you're looking for NOS 6L6s on a budget, I recommend the 6BG6G with 6L6 adapters. The 6BG6G is the same tube as the 6L6G, except with a top cap and different pin-out for use in TV sets. Even with the necessary adapters, you could get them for cheaper than a pair of vintage 6L6Gs with a little shopping. I bought the adapters as DIY kit from http://www.vacuumtubes.com/6BG6.html, and there are prebuilt adapters available from eBay.

I'm using Tung-Sol 6BG6Gs in my amp, shown here with a Telefunken ECC803S preamp tube. The biasing in the APPJ works quite well, at least for the preamp tube- my ECC803S is extremely weak, to the point I can't bias it in one of my other amps, but it works fine (and sounds stellar!) here.

At a glance, that looks an awful lot like the PA1502A's board, down to the grey coupling caps and Nichicon cathode bypass caps. I've replaced those caps in my amp and the improvement in, well, everything, was crazy! There's a future upgrade if OP gets bored with tube rolling.

Excellent information, all. Thanks!

 

[GuyNoir]

After some cursory research, the KT66 should be a shoe-in. Slightly less heater current and output than an EL34.

 

[CZ4A]

I have the APPJ PA0901A using 6bq5's and was thinking about doing a capacitor upgrade. Is the board up to snuff to de-soldering without self destructing?

I had no issues with (de)soldering in my PA1502A. I replaced the 0.1uf coupling caps with WIMA MKP4 0.47uf and the 220uf cathode bypass caps with 1000uf aluminum polymer caps. Some folks in the Head-Fi thread for the PA1502A use boutique caps. The speaker amps based on this circuit have more space for physically larger caps, but in terms of capacitance 0.33uf or 0.47uf coupling/1000uf bypass work best.

https://www.head-fi.org/threads/any-opinions-reviews-on-gemtune-appj-pa1502a.780178/page-19
https://www.aradiogurl.net/hhjournal/2016/06/01/gemtune-pa1502a-appj-headphone-tube-amp-mod/

 

[Tim64]

Thanks for the responses, I have done a couple partial recaps on a receiver and a amp plus some repair work, I have learned just because a board looks really good does not mean a trace wont lift if you look at it cross eyed. I most likely will open up the APPJ in the near future and get to work on it.

 

[primosounds]

Do you feel lucky? It looks pretty delicate to me, though I'm sure a deft and experienced hand will prevail. That rules me out.

There is a less intrusive method of recapping a circuit board that doesn't require desoldering. It is the method that was taught back in the day for tv/radio repair men/women. You simply cut the lead at the capacitor or resistor body..then put a small loop in the wire, guide the lead from the new part thru the loop, pinch the loop, loop the new lead, pinch it, then solder the joint, finally flush cut the excess lead.. For very old , first generation circuit boards, this is actually the best way to change components and is far less likely to damage the delicate foil traces.

 

[Oreo61]

For me most mods make a slight improvement or no discernible improvement at all. Well, on my APPJ El34 amp I replaced the 220uf cathode bypass caps with 1000uf Elna Silmic II, bypassed with Vishay-Roderstein 1837 .1uf caps .Replaced coupling caps with Mundorf EVO Aluminum Oil .33uf caps. Replaced volume pot with Alps Blue. This was already an amplifier punching above it's weight, now it doesn't struggle at all with the frequency extremes, lending a naturalness to the sound. Highly recommended mods, total parts cost was $40.00. Tube complement is two Electro-Harmonix EH6CA7, and a Genalex Gold Lion 12ax7.

 

[pegasus]

Replaced coupling caps with Mundorf EVO Aluminum Oil .33uf caps.

I'm going to replace those caps but I can't identify for sure what actual caps values are ( see attached pic ). Can anyone help me identify correct caps value ?

 

[pegasus]

They're EVOX MMK caps ( 120nJ400 value ?? )