| w5jag |
I just bought one of these little guys a few minutes ago.
A web search turned up nothing, anyone know anything about them?
I bought a Hammond chassis and some el34 and 6ca7 (should be in tomorrow) and was going to scratch build a single ended amp, but saw this and thought I might save myself a bit of trouble.
regards,
Win |
|
|
| andrew_whitham |
which little guy's? :D
Andy |
|
|
| Geek |
I've seen those!
They are mass produced in China and for a small fee, they put your company name on them. Not likely you'll find info on it under that name.
One of my wholesaler's offered them to me. They didn't say who made them though. |
|
|
| bassrogue |
| I had my eyeball on that amp the other day too but didnt buy. Please let us know how it sounds and build quality.:drink: |
|
|
| andrew_whitham |
ahhhh not the same then,
my experiences with a Chinese SE amp are in this thread
http://www.diyaudio.com/forums/show...&threadid=92509
Since the thing is not available to me in the UK I can't see the larger pictures (I assume thats it) only the thumbnails, Out of interest what are the driver tubes?
It looks like the box on the one you got is physically larger which will be a heck of a benefit. You'll see I ultimately got something I was reasonably happy with. Not that it sucked out of the box you understand.
Depending on how confident you feel (and if you were doing a scratch build then it should be no problem) you might find the EL34's you got can be dropped right in - I'd suggest you give them a go but it depends on the biasing arrangements in your amp.
Andy |
|
|
| w5jag |
The photo shows EH 12ax7 and Reflector/Sovtek KT88.
I had some JJ E34L (blue) come in today. I'm expecting some Ei 6ca7 to come in tomorrow. |
|
|
| w5jag |
The photo shows EH 12ax7 and Reflector/Sovtek KT88.
I had some JJ E34L (blue) come in today. I'm expecting some Ei 6ca7 to come in tomorrow. |
|
|
| andrew_whitham |
| quote: | Originally posted by w5jag
I had some JJ E34L (blue) come in today. I'm expecting some Ei 6ca7 to come in tomorrow. |
Curses! I'm a bit jealous..
JJ E34L's did a lovely job in mine but the pins are small far less tight than the EH KT88's they replaced. If you have them try that before you do anything else (I have rk=300R biases out at 22v I think, I remember its 25.6 watts. off the 25 watt rated tube - no problems) I was Uber pleased with the result. I'll emphasise that a 5k OPT with the KT88 is odd you may have something that better suits that tube.
I'm real interested in this. The size of the case in mine was a real handicap which you dont have. I reckon you'll have a good performer out of the box. Imagine if you start adding ccs's and a regulated PSU :bigeyes:
Keep us posted, I'm in China till April and I have room in my case...
Andy |
|
|
| w5jag |
Thanks, Andy.
The first thing I am going to do is open up the amp and make sure pin 1 on the KT88 socket is not being used as a tie point. If it is not, I'll jump it over to pin 8 as I do intend to use the E34L or 6CA7 right off the bat.
I am really curious to see how the little thing is made and wired. With a 10 watt rating, I'm guessing it is wired as an SET, but maybe not. I bought it on a lark because it was so cheap, but now I am getting really anxious to see it in person. So far, the seller has not responded to my e-mails about a shipping date, so I'm not real pleased about that. :mad:
I still intend to scratch build an amp to play with. After 30 years of ham radio, I have hundreds, maybe thousands, of tubes and parts, from 45's all the way up to 572B (just no 6CA7 - figures since that is what I decided on to play with).
Do you have a suggestion as to what to replace the 12AX7 with? I was thinking of RCA 7025, but I have nearly all of the other brands and types, including Telefunken, Mullard, Amperex, etc. ....
Regards,
Win |
|
|
| andrew_whitham |
| quote: | Originally posted by w5jag
The first thing I am going to do is open up the amp and make sure pin 1 on the KT88 socket is not being used as a tie point. |
Tie pin, good point, on mine it was already linked to pin 8
Did you get anywhere with the seller
Definately a SET amp it says so in the ad ;) plus a PP kt88 would be of the order of 50 watts I think?
Your options for the 12AX7 might be more varied than you think, it depends what its doing. Maybe it's paralleled? or part of a more complex circuit (mu follower?)
I'd also imagine its run from 6.3v not 12.6 possibly stolen from the same supply as the KT88's
I approached mine from the stand point of having 2 tube sockets to play with, It'll depend on how much surgery you're willing to do.
A straight swap? Well it sounds like you have plenty of scope for testing ;-) and certainly more experience of this type. (I'd never even HEARD of a 7205!)
Depending on the voltages present I'd personally favour an ECC88 in there - I like it and the mu of 33 will present the KT88 with enough voltage swing from a 2v source.
In fact, the choice of the 12AX7 is suddenly strange mu=100 right?, maybe there's global F/B already? I'm using 6J5GT's in my octal setup and the actual gain is about only 15. Hmmmm
Hope it arrives soon, and you'll tell us all about it.
Andy |
|
|
| w5jag |
| quote: | Originally posted by andrew_whitham
1) Did you get anywhere with the seller
2) Definately a SET amp it says so in the ad
3) In fact, the choice of the 12AX7 is suddenly strange mu=100 right?, maybe there's global F/B already? I'm using 6J5GT's in my octal setup and the actual gain is about only 15. Hmmmm
Hope it arrives soon, and you'll tell us all about it.
Andy
|
1) Nope. Four emails and one telephone call to an answering machine have yielded only one cryptic, semi intelligible, and completely uninformative email reply.
2) I guess I was a bit cryptic; by SET I meant single ended triode, as I expect they have wired the KT88 as a triode but maybe not. When I get it, obviously I can report on this.
3) A real 7025 is a 12AX7A with a spiral filament for lower hum in sensitive applications like a phono stage. A 12AX7 seems like a lot of gain that I likely will not need. I will be driving it from the preamp out of a Yamaha a/v receiver, so I have plenty of drive. I also have lots of 5751, 12AZ7, 12AY7 (I think), 12AU7, and 12AT7 to play with. I am assuming the Euro ECC88 number you cited translates to our 12AU7 type.
My Ei 6CA7 came in yesterday. This is an impressive looking tube and makes the JJ E34L look downright dainty.
I'm going to spend the afternoon punching some octal holes in an old aluminum chassis to start working on the E34L/6CA7 proto!
Best regards,
Win W5JAG |
|
|
| PeteM |
| quote: | | My Ei 6CA7 came in yesterday. This is an impressive looking tube and makes the JJ E34L look downright dainty |
Many of those Ei 6CA7's are "downright" flaky too. QA on later tubes was none existent at best. |
|
|
| w5jag |
| quote: | Originally posted by PeteM
Many of those Ei 6CA7's are "downright" flaky too. QA on later tubes was none existent at best. |
I bought four, and they all look pretty good. They seem hard to find over here now - hardly anybody lists stock on them. If they are flaky like you say, maybe that is a good thing!
I was very impressed with the robustness of the structure and thickness of the bulb glass. I have a lot of experience with RF tubes and miniature / octal receiving tubes, but nothing with audio tubes other than common multi use stuff like 6L6, 6V6, etc. At present, I have nothing that uses 6CA7 so all I have been able to do is jump power to the filaments to see if they light up.
If I get some time later, I'll put them on the TV-7/D to make sure they at least conduct!
Regards,
Win W5JAG |
|
|
| PeteM |
| quote: | | They seem hard to find over here now - hardly anybody lists stock on them |
They are difficult to find here too, I know of one supplier but they are not original boxed Magnoval branded IMHO were the best of the bunch.
| quote: | | I was very impressed with the robustness of the structure and thickness of the bulb glass |
Hopefully yours will be OK. ;) |
|
|
| w5jag |
| quote: | Originally posted by PeteM
They are difficult to find here too, I know of one supplier but they are not original boxed Magnoval branded IMHO were the best of the bunch.
Hopefully yours will be OK. ;) |
Mine are in the Magnoval boxes. Even have a touch of corrosion on the pins. Maybe they are old timers! |
|
|
| w5jag |
Should arrive at my office on Friday, March 9!
Hopefully, I will have more details on this amp this weekend.
Win W5JAG |
|
|
| andrew_whitham |
| quote: | Originally posted by w5jag
2) I guess I was a bit cryptic; by SET I meant single ended triode,
|
er no actually I was being dumb. It'll be SE of some sort :o
| quote: |
3) I am assuming the Euro ECC88 number you cited translates to our 12AU7 type. |
ECC88 = 6DJ8 common as muck standard dual triode, but Its not directly compatible or comparable with the 12AX7. I just happen to like it, Its familiar now...
direct plug ins that I can think of are
12AU7 is an ECC82, (mu = 18?)
12AT7 is an ECC81 (mu = 60)
probably many more too. (thats stating the obvious a little isn't it)
Good luck with the amp - I too am now looking for a pair of the EI 6CA7's - it was the big bottle comment that did it... :)
Andy |
|
|
| w5jag |
It finally came in today, and this amp is a bargain.
The first point of interest is that the shipping container identifies the product as made in USA. It was well packaged with manufacturer labelled inner and outer boxes, a foam suspension, and a thick plastic bag for the amp itself. It comes with a power cord, and a robust set of phono cables, and speaker cables. All of the tubes are installed; the amp is ready to be plugged in right out of the box.
There is a manual supplied, but no schematic. The chassis looks good, feels rigid, and where appropriate, fasteners are countersunk.
Weight is twenty pounds. Not shown in the pictures on Ebay are a heavy duty perforated cover to shield the tubes from prying fingers. When I removed both of the covers, I found a toroidal pwr xfmr, and a pair of appropriate looking OP trannies. The trannies are open frame, and there are no ultralinear taps on the primaries. There is no country of origin listed on these parts, so they are likely US made.
Pulling a tube, I can see the KT88 sockets are attached to a PCB, but they are solidly attached indeed. There is no give or play at all and the tube sockets have a tight grip on the pins.
The tube complement is a Chinese Valve Art 5AR4 rectifier, (2) EH 12AX7, and (2) Sovtek Reflector KT88's with date codes of 99 06 and 99 08. The front panel input switch and volume control feel good.
Here are a few highlights from the manual:
Single ended, Zero feedback design;
Automatic biasing circuit;
RelCap PPFXS (whatever these are) for coupling capacitors;
Oil type capicitors used extensively;
Non Magnetic brushed stainless steel chassis
Hopefully I can get it on the workbench in the ham shack later this week to remove the bottom and see more of its construction.
I wonder if this is from a manufacturer that went belly up and its finished product was liquidated cheap in a bankruptcy sale. There is no way this product could have been manufactured anywhere and sold profitably for $299. |
|
|
| crispycircuit |
| Nice find. Post some pics. $299?? What the hey!! |
|
|
| Robert McLean |
| I notice in the ebay pictures that there are 2 input jacks for each channel. Why is that ? Just curious. |
|
|
| w5jag |
I brought it home tonight and opened it up on the bench. This is really a nice little amp and certainly looks to be domestically manufactured!
The tube shield and transformer covers have a nice spatter paint finish. If you have ever seen the old Drake tube ham gear, the finish is near identical. The chassis is robust and spot welded at the corners making a very solid and rigid platform for the amp. All of the fastener holes are nicely finished, and the fasteners are high quality. The knobs feel to be solid aluminum.
The PCB is a silk screened, double layer, fiberglass board marked Sound Creative - USA.
All of the tube sockets have gold plated pins. The output binding posts, input phono jacks, and input switch contacts are gold plated. The input switch has a very positive snap action. The input pot is a sealed Alps 250K unit. All of the resistors (where I can see a brand) are Dale metal oxides, the cathode resistors are 300 ohm 10W ceramic wirewound units. The electrolytics are 450 volt Jamicons. The coupling caps from the 12AX7's to the KT88's are .22 uF oil Multicaps. The wiring looks to be around 18 gauge stranded, marked Pacific brand.
The unloaded plate voltage (all tubes except 5AR4 removed) is 360 volts at the KT88 plate pin. The markings on the PCB suggest that the OPT primary is 3.5K. The power supply looks to be sort of a quasi monoblock design. There is a single, hefty, input choke, a large (unmarked), looks to be dual section, oil filled filter capacitor, and each channel has two 47uF electrolytics in parallel on the PCB.
I didn't spend much time trying to figure out the topography for the drivers. The KT88's are wired as triodes. Although the PCB has component locators for a parasitic supressor between the screen and plate, this unit has the screen and plate bridged with a jumper.
Pin 1 on the KT88 sockets is open. Although the manual goes to great lengths to indicate that nothing but KT88's can be used in the amp, what fun is that? Pins 1 and 8 will get bridged tomorrow night to open up the tube selection. I'd like to try the E34L's / 6CA7's I have, but that 300 ohm cathode resistor makes me a little uneasy at the plate dissipation :hot: for these smaller tubes.
All in all, this looks like quite the deal for the price tag. Although I see they have now taken a price jump, the amp still looks to be an excellent value given the quality of the components and construction. |
|
|
| w5jag |
| quote: | Originally posted by diegot
pics please ;) |
Tomorrow! |
|
|
| w5jag |
| quote: | Originally posted by w5jag
Tomorrow! |
Some pics I took with my cell phone. Hope they appear.
Win W5JAG |
|
|
| Robert McLean |
| quote: | | I notice in the ebay pictures that there are 2 input jacks for each channel. Why is that ? Just curious. |
OK, I see now one of the knobs is an input switch, I thought they were both volume controls for some reason. :confused: |
|
|
| andrew_whitham |
| quote: | Originally posted by w5jag
Pin 1 on the KT88 sockets is open. Although the manual goes to great lengths to indicate that nothing but KT88's can be used in the amp, what fun is that? Pins 1 and 8 will get bridged tomorrow night to open up the tube selection. I'd like to try the E34L's / 6CA7's I have, but that 300 ohm cathode resistor makes me a little uneasy at the plate dissipation :hot: for these smaller tubes.
|
Hi,
I think that the 300 ohm resistor is usable. but :hot:
I use that value in my SE amp, (with a 5K transformer - granted) measures at about 22v bias when I put in the EL34's the plate dissipation is right on the dotted line!
If my working is correct you'll get around the 25W mark, right? (or maybe JUST over?)
The bigger bottle E34L's I use (JJ) seem quite happy so far at 26w dissipation, If I remember. Definately worth a try though - I was so impressed with the results that I haven't gone back to the KT88's
Just my two cents... theres a LOT of personal perference in there.
Reckon that you got a bargain with them though, whatever you choose to do, verrrry nice. If they sound like they look....
Andy |
|
|
| w5jag |
Andy,
The plate dissipation looked like it would be close, but I jumped pins 1 and 8, held my breath, and fired it up with the JJ E34L's. It worked fine. The plates are not showing any color at all.
I didn't take any further voltage measurements - apparently the B+ loads down enough to keep the E34L tubes from frying but they are probably close to their limits. If I have a premature failure of one of the E34L's, I'll take another look at it or just put the KT88's back in.
Piddling around with some tubes in it, I thought that straight out of the tube carton, the Ei 6CA7's sounded better than the E34L. I have some Siemens 12AX7 marked as Westinghouse in the driver positions. I also tried some JAN GE 12AT7 :xeye: and thought they sounded pretty good.
Win W5JAG |
|
|
| andrew_whitham |
Hi,
no, No, not jealous you cant get these here at all, :bawling:
Anyway, depending on how comfortable you are on measuring voltages on a live amp (better - how are you for crocodile clip equipped test leads) measure the voltage across the 300ohm resistor and the plate voltage
or if you have already please tell!
I measured some odd (OK unpredicted) voltages on mine and I couldnt account for the discrepancy, must be down to the internal workings of the tube (or I cant do math for toffee :) ) but dissipation was less than I expected. Your lower impedance trafo ought to drive them a 'tadge' harder though?
(tadge = old english word equivalent to 2/3 of a smidgin)
BTW Tubelab is the one for getting plate glow, I think that hes had the JJ E34L's well "outside the envelope" If he's watching he might tell us the dissipation he got...
Really MUST get some of those EI tubes - I'm IN China so you'd think... $
But I admit I'm a bit distracted these days by the sensual curves of a Sovtek KT88 ;)
Cheers
Andy |
|
|
| mj23 |
| quote: | Originally posted by w5jag
All in all, this looks like quite the deal for the price tag. |
Hi, very nice inside out description of this amp, but nothing about the sound, so is it good? comparable to entry level Audion Sterlings? (they look verrry similar! PCB, same tubes, SE).
I am getting this amp, sound creative, next week, can not wait to see how it sounds. it appears to be promising!
One question, will I be able to put el34's without any modifications? I have no diy skills with tube amps..
Also, is it possible to make it work on 220 voltage? thinking to send it to europea relatives if its good.
thank you for your answers...
ps.: i was searching a lot of time for tube amp on ebay, and somehow just like you stick on this one;)
mj23 |
|
|
| w5jag |
| quote: | Originally posted by mj23
Hi, very nice inside out description of this amp, but nothing about the sound, so is it good?
----------
One question, will I be able to put el34's without any modifications? I have no diy skills with tube amps..
-----------
Also, is it possible to make it work on 220 voltage? thinking to send it to europea relatives if its good.
mj23 |
I'm not an audiophile, so I didn't try to get into subjective descriptions about the sound. I think it sounds great for its price. In my setup, it's being driven by the preamp outs of a newer Yamaha a/v receiver. It definitely sounds better than the PA in the Yamaha.
I didn't like the sound of the Electro Harmonix 12AX7 tubes at all. I tried some Telefunken 12AX7, Mullard 12AX7, Siemens 12AX7,and several sets of JAN GE 12AT7 in it and all sounded vastly better than the EH tubes. Right now I have a tightly matched set (section to section and tube to tube) of 1957 manufacture JAN GE 12AT7's in it.
The JJ E34L's sounded better than the Sovtek KT88's, but, with good driver tubes, the Sovteks are fine. I have the Sovtek's in mine at the moment.
To use E34L's, EL34's, 6CA7's, 6550's or similar, you need to install a jumper between pins 1 and 8 on the KT88 sockets. This will tie the suppressor grid to the cathode. This connection is made inside the tube in the KT88.
A 220 tap on the xfmr was not immediately obvious to me; but I really didn't look for one.
It's a nice looking amp, and I hope you enjoy yours as much as I am enjoying mine.
Win W5JAG |
|
|
| mj23 |
| quote: | Originally posted by w5jag
To use E34L's, EL34's, 6CA7's, 6550's or similar, you need to install a jumper between pins 1 and 8 on the KT88 sockets. This will tie the suppressor grid to the cathode. This connection is made inside the tube in the KT88.
Win W5JAG |
I finally got it! Looks nice! But I am not very satisfied with sound so I want to try EL34 tubes...and I need your help..
Heres the picture of inside, please tell me on which pins should I install jumper? which one is 1 and which one is 8?
Will I be able to use kt88 again or in this case i will have to remove jumpers?
thanks!!! |
|
|
| w5jag |
| quote: | Originally posted by mj23
Heres the picture of inside, please tell me on which pins should I install jumper? which one is 1 and which one is 8?
Will I be able to use kt88 again or in this case i will have to remove jumpers?
thanks!!! |
If you are not certain about locating tube pins, it might be best not to be inside of the amp with a soldering iron.
If you want to try it anyway, the key of the octal socket separates pins 1 and 8. Locate the key and you know where pins 1 and 8 are. Use an ohmmeter from the tube socket to the PCB to make sure you have the right pins located on the trace side of the board. The jumper you see installed from the factory is between pins 3 (plate) and 4 (screen grid). The filaments are at 2 and 7.
By jumping Pins 1 and 8, you are making a connection from the supressor grid (pin 1) to the cathode (pin 8) for those tubes that do not have an internal connection. The KT88 has the cathode and suppressor connected internally, so could care less whether the jumper is or is not there.
Good luck!
Win W5JAG |
|
|
| w5jag |
| quote: | Originally posted by andrew_whitham
Anyway, depending on how comfortable you are on measuring voltages on a live amp (better - how are you for crocodile clip equipped test leads) measure the voltage across the 300ohm resistor and the plate voltage
or if you have already please tell!
|
Andy,
I finally got the shack cleaned up enough to bring the amp back out and take some measurements. Unfortunately, most of my tubes are stored elsewhere, but here is what I could measure.
Rectifier is a fresh NOS GE 5AR4, line voltage in the shack is 122 volts, cathode resistor is 300 ohms. I put a 6.8 ohm load on the speaker terminals. Drivers are GE JAN 6201/12AT7W, 1957 vintage, extremely tightly matched section to section and tube to tube, they are virtual identical twins. In looking at the driver circuitry, the sections of each tube appear to be in parallel.
"Mullard" EL34 reissue:
loaded plate voltage 292; cathode voltage 19.8 volts; 67 mils plate current and 18.2 watts dissipation if my math is correct. These tubes are loafing, but the way the glass creaks you would think otherwise. They sound very good in my opinion, but I wish to emphasize (again) I am not an audiophile.
JJ 6V6S. I know it sounds crazy, but I had these on hand, so what the hey:
loaded plate voltage 300; cathode voltage 15.9 volts; 53 mils plate current and 15 watts dissipation. If I read the JJ data sheet correctly, the rating is 10 watts in triode mode. I guess that is following the Tubelab tradition of running 'em hot . Surprisingly, after about 25-30 hours of use (abuse) the only sign of trauma on the 6V6S is a small dark spot on one of the plates. In operation, the 6V6S appears to be in no distress at all, and, but for these measurements, I would have thought they were loafing.
The JJ 6V6S sounds really good, even though the plate load is way too low. This is really an impressive tube in my noob opinion, and I would not bother with NOS 6V6 given the quality of this tube. All of my NOS 6V6GT, GE and Tung Sol, are going into my for sale inventory.
Regards,
Win W5JAG |
|
|
| alexg |
Why does the grid suppressor needs to be connected to the cathode?
I did Mikael's KT88 SE amp and when I use EH EL34, on it the hum is very loud. (pin 1 and 8 on the KT88 sockets are not tied).
Would tying the grid suppressor and the cathode cure this hum problem?
Thanks. |
|
|
| w5jag |
The supressor grid of the EL34 should not just float unconnected.
I would connect it to the cathode.
Win W5JAG |
|
|
| drjlo |
Any long term impressions on this amp, especially sound quality compared to other similar amps?
Anybody's amp malfunction or break down? TIA. |
|
|
| w5jag |
After I built my SimpleSE, I gave cheap Ebay KT88 amp to my guitar playing, perpetual college student, nephew last Thanksgiving as an upgrade to the AES 11BM8 P-P amp he was using.
I also sent a big box of different sets of 12AT7, 12AX7, 6550, KT88, 6L6, 5AR4, and, at the time, almost all of my stock of 6V6 for his guitar amp, so he's set for tubes until he is well into middle age.
You know how kids are - he didn't come home for Christmas, and I haven't heard back from him. I can only assume it's working fine, or he tried to play his guitar through it and fried it, and does not want to tell me.
It was a nice amp; an incredible bargain at the price.
Win W5JAG |
|
|
|
