Great ! Just replaced a flaked input cap... VSWR still off the scale on 20,
still with 100 W CW the loading has improved to 500mA @ 2500V 400 mA with
RTTY 2 tone. I guess that will be the top limit of the wimpy PSU.....
Also found that one of the 4-400s is dud (need to get another one) so the
tube replacement test is postponed.
Rahul
On Thu, Sep 10, 2009 at 10:24 PM, Carl <km1h@jeremy.mv.com> wrote:
> It all depends on plate voltage and the brand of tube. It was never
> designed for GG so it hasnt been characterized until much later. My newest
> Eimac spec sheet is a 1966 revision and the 3-400Z was already on the
> market.
>
> You will have to experiment.
>
> Directly grounding the grids will give a bit more output, result in less
> stability and result in around 3 dB worse IMD in dynamic voice tests (not a
> static 2 tone)
>
> Carl
>
>
>
> ----- Original Message -----
> *From:* Rahul Sathe <vu3raz@gmail.com>
> *To:* Carl <km1h@jeremy.mv.com>
> *Sent:* Thursday, September 10, 2009 9:42 AM
> *Subject:* Re: [Amps] SB221 Low Power Help
>
> Carl,
> I think the 4-400 is Zero Bias, do I still need a string of diodes or if
> just bypass the zener it should work ?
>
> I also seen people suggesting to ground the grids of 3-500 to reduce the
> drive requirements and this will increase IMD.. I am a bit skeptical. I will
> have to test IMD on a Spectrum Analyzer before i can really ground the grids
> directly. Have you ever grounded the grids directly? what effect it has?
>
> Too many questions, I hope i am not too curious ;)
>
> Regards /// Rahul
>
> On Thu, Sep 10, 2009 at 6:26 PM, Carl <km1h@jeremy.mv.com> wrote:
>
>> The 4-400A requires a little bit more drive than the 3-500 so the grids
>> can be directly grounded if you wish. 100W drive should still give 1000W+
>> out in SSB position.
>>
>> Carl
>>
>>
>>
>> ----- Original Message -----
>> *From:* Rahul Sathe <vu3raz@gmail.com>
>> *To:* Carl <km1h@jeremy.mv.com>
>> *Sent:* Wednesday, September 09, 2009 10:09 PM
>> *Subject:* Re: [Amps] SB221 Low Power Help
>>
>> Thanks carl, I have already replaced the stock fan with a high speed high
>> volume fan. What about the grid chokes? I guess 4-400 do not need them?
>>
>> Regards /// Rahul
>>
>> On Thu, Sep 10, 2009 at 7:24 AM, Carl <km1h@jeremy.mv.com> wrote:
>>
>>> Enough to obtain the same idle current. The zener can be replaced by a
>>> reverse string of 1N5408's and the correct number by experimenting.
>>>
>>> If you intend to run them at full power another fan should be used as its
>>> not adequate at 50 Hz. Harbach sells a high speed replacement in the US
>>> which is ideal for graphite plates and should be OK in India also.
>>>
>>> Off to bed.
>>>
>>> Carl
>>>
>>>
>>> ----- Original Message -----
>>> *From:* Rahul Sathe <vu3raz@gmail.com>
>>> *To:* Carl <km1h@jeremy.mv.com>
>>> *Sent:* Wednesday, September 09, 2009 9:37 PM
>>> *Subject:* Re: [Amps] SB221 Low Power Help
>>>
>>> Carl
>>> How much bias I need on 400s? any other changes required for long term
>>> use, ls 130V cut off ok?
>>>
>>> Rahul
>>>
>>> On Thu, Sep 10, 2009 at 7:01 AM, Carl <km1h@jeremy.mv.com> wrote:
>>>
>>>> The 4-400's will at least tell you if something dramatic changes with
>>>> the power. Its better than spinning wheels working in the input. Get the
>>>> most obvious fault out of the way first.
>>>>
>>>> They may require a bias change for long term use but not just to test.
>>>> No socket changes. Filaments are identical.
>>>>
>>>> Carl
>>>>
>>>>
>>>>
>>>> ----- Original Message -----
>>>> *From:* Rahul Sathe <vu3raz@gmail.com>
>>>> *To:* Carl <km1h@jeremy.mv.com>
>>>> *Sent:* Wednesday, September 09, 2009 8:45 PM
>>>> *Subject:* Re: [Amps] SB221 Low Power Help
>>>>
>>>> Carl,
>>>>
>>>> I have few brand new european 4-400 s however I have not got time to
>>>> test them in the amp. With a normal Idle current in the present 3-500s I
>>>> would first try and look in the input circuit.. I still suspect that the
>>>> 100
>>>> W is not reaching the cathode... if it does not work.. i will replace the
>>>> tubes with 4-400, but I do not know if I can "just replace" them.
>>>>
>>>> Regards /// Rahul
>>>>
>>>> On Wed, Sep 9, 2009 at 11:10 PM, Carl <km1h@jeremy.mv.com> wrote:
>>>>
>>>>> Id be suspecting the tubes by now but dont know if you have access to
>>>>> any in India. 4-400's or Euro equivalents can also be used in a "pinch"
>>>>> and
>>>>> the input realigned as needed.
>>>>>
>>>>> Carl
>>>>> KM1H
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> ----- Original Message -----
>>>>> *From:* Rahul Sathe <vu3raz@gmail.com>
>>>>> *To:* Carl <km1h@jeremy.mv.com>
>>>>> *Sent:* Tuesday, September 08, 2009 9:13 PM
>>>>> *Subject:* Re: [Amps] SB221 Low Power Help
>>>>>
>>>>> Carl, No sign of melted contacts on the switch. The chokes are equal
>>>>> spaced and not open. the caps look ok on a VTVM no leakage (I still think
>>>>> these need replacement). Will replace these soon.
>>>>>
>>>>> One of the Caps in the drive chain, on the cathode found to be flaking
>>>>> along the leads when i moved it now replaced it with a new....will test it
>>>>> today evening after morning qth work. if things are same then time to move
>>>>> to internal coax.
>>>>>
>>>>> Gerald, I fully agree with you. I am not in a favor of using the ATU as
>>>>> the purpose of having a built in ATU is totally different. I used to have
>>>>> a
>>>>> HW 101, I also think that it would have been easy to match and drive 220 /
>>>>> 221 with its sibling easily.
>>>>>
>>>>> Regards /// Rahul
>>>>>
>>>>> On Wed, Sep 9, 2009 at 12:41 AM, Carl <km1h@jeremy.mv.com> wrote:
>>>>>
>>>>>> Grounding the grids isnt any help.
>>>>>>
>>>>>> With that idle it appears that both tubes are working to some degree.
>>>>>>
>>>>>> The grid chokes are 3 pie's and should be equally seperated. It they
>>>>>> are touching it is a sign of a tube gas arc. Also carefully inspect all 6
>>>>>> grid capacitors for cracking. If you have a good analog VOM or VTVM check
>>>>>> for leakage.
>>>>>>
>>>>>> Carefully look at the input and output switch for melted contacts.
>>>>>>
>>>>>> If the power falls off as frequency goes up that is often a sign of
>>>>>> weak tubes. Do you know the history of the amp? When did it last work
>>>>>> 100%?
>>>>>>
>>>>>> Carl
>>>>>> KM1H
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> ----- Original Message -----
>>>>>> *From:* Rahul Sathe <vu3raz@gmail.com>
>>>>>> *To:* Carl <km1h@jeremy.mv.com> ; amps@contesting.com
>>>>>> *Sent:* Tuesday, September 08, 2009 1:39 PM
>>>>>> *Subject:* Re: [Amps] SB221 Low Power Help
>>>>>>
>>>>>> Carl,
>>>>>> Plate Idle Current in SSB position is ~ 120 to 125 mA. I have to check
>>>>>> the grid chokes as suggested by you, how abt grounding the grids directly
>>>>>> without chokes?
>>>>>>
>>>>>> Checked the tubes... there is no short.
>>>>>> The coaxial cables looks ok, as the VSWR is far better on other bands
>>>>>> like 40 and 80 input can be tuned on 40 and 80.
>>>>>>
>>>>>> Will run the amp with individual tubes as suggested by dan.
>>>>>> I am not sure if it is a European build, however it is wired for 230 V
>>>>>> no way to find out if it has 50Hz transformer.
>>>>>>
>>>>>> Thanks for all the help.
>>>>>>
>>>>>> Regards /// Rahul
>>>>>>
>>>>>> On Tue, Sep 8, 2009 at 10:50 PM, Carl <km1h@jeremy.mv.com> wrote:
>>>>>>
>>>>>>> A couple of things to check Rahul:
>>>>>>>
>>>>>>> 1. Plate idle current should be 120-150 ma in the SSB position.
>>>>>>>
>>>>>>> 2. One of the grid chokes is open from a tube arc or short.
>>>>>>>
>>>>>>> 3. If it has always been this way since built the coax cables going
>>>>>>> to the input bandswitch may be reversed.
>>>>>>>
>>>>>>> Input VSWR is a function of plate current & voltage so with one
>>>>>>> defective tube it will be quite high and out of the networks tuning
>>>>>>> range.
>>>>>>>
>>>>>>> Dont go ripping things out, that 100W should be more than enough at
>>>>>>> 1000W out.
>>>>>>>
>>>>>>> Also, unless it is a European built/kit amp from Heath UK, or
>>>>>>> supplied with a 50 Hz transformer it will have to be run at reduced
>>>>>>> power to
>>>>>>> keep the transformer from burning up.
>>>>>>>
>>>>>>> Carl
>>>>>>> KM1H
>>>>>>>
>>>>>>>
>>>>>>> ----- Original Message ----- From: "Rahul Sathe" <vu3raz@gmail.com>
>>>>>>> To: <amps@contesting.com>
>>>>>>> Sent: Tuesday, September 08, 2009 11:32 AM
>>>>>>> Subject: [Amps] SB221 Low Power Help
>>>>>>>
>>>>>>>
>>>>>>> Hello Experts,
>>>>>>>>
>>>>>>>> My name is Rahul call VU3RAZ. This is my first post to the list. I
>>>>>>>> am
>>>>>>>> seeking help on fixing my old SB221.
>>>>>>>>
>>>>>>>> as such the amp works on all bands, no arc or parastatics, tuning
>>>>>>>> and
>>>>>>>> loading is smooth and easy.. I am not able to load the amp to full
>>>>>>>> rated
>>>>>>>> plate current even with a 100 W drive with my 756 Pro3. Input VSWR
>>>>>>>> is high,
>>>>>>>> I tried tuning the input tuned circuit but no luck on few bands (20,
>>>>>>>> 15).
>>>>>>>> With the 756 ATU the things improve but I can not get plate current
>>>>>>>> beyond ~
>>>>>>>> 400 mA. Even tried disconnecting HT from each tube to see if one if
>>>>>>>> the
>>>>>>>> 3-500 is dead... both work but even with single tube I am not able
>>>>>>>> to load
>>>>>>>> the amp fully. Am I looking at dead (weak) tubes ... can both of
>>>>>>>> them show
>>>>>>>> exact same behavior? Or I am missing something I am not sure if I
>>>>>>>> need to re
>>>>>>>> build the PSU (replace caps)
>>>>>>>>
>>>>>>>> Please help...
>>>>>>>>
>>>>>>>> 73
>>>>>>>> DE VU3RAZ
>>>>>>>> _______________________________________________
>>>>>>>> Amps mailing list
>>>>>>>> Amps@contesting.com
>>>>>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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